Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $234.75   3.492%   $242.9475   $242.95   $242.95   $242.90  
  Purchase #2 $217.30   9.571%   $238.0978   $238.10   $238.10   $238.10  
  Purchase #3 $242.86   13.843%   $276.4791   $276.48   $276.50   $276.50  
  Purchase #4 $166.49   6.667%   $177.5899   $177.59   $177.60   $177.60  
  Purchase #5 $149.99   13.292%   $169.9267   $169.93   $169.95   $169.90  
  Purchase #6 $146.65   9.607%   $160.7387   $160.74   $160.75   $160.70  
  Purchase #7 $192.61   7.789%   $207.6124   $207.61   $207.60   $207.60  
  7 purchase totals = $1,350.65       $1,473.3921   $1,473.40   $1,473.45   $1,473.30