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 $84.33   10.625%   $93.2901   $93.29   $93.30   $93.30  
  Purchase #2 $216.33   7.509%   $232.5742   $232.57   $232.55   $232.60  
  Purchase #3 $64.28   3.779%   $66.7091   $66.71   $66.70   $66.70  
  Purchase #4 $178.39   9.469%   $195.2817   $195.28   $195.30   $195.30  
  Purchase #5 $159.93   10.709%   $177.0569   $177.06   $177.05   $177.10  
  Purchase #6 $250.64   13.351%   $284.1029   $284.10   $284.10   $284.10  
  Purchase #7 $44.69   7.204%   $47.9095   $47.91   $47.90   $47.90  
  7 purchase totals = $998.59       $1,096.9244   $1,096.92   $1,096.90   $1,097.00