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 $189.47   5.703%   $200.2755   $200.28   $200.30   $200.30  
  Purchase #2 $227.79   10.410%   $251.5029   $251.50   $251.50   $251.50  
  Purchase #3 $102.31   8.351%   $110.8539   $110.85   $110.85   $110.90  
  Purchase #4 $32.40   8.735%   $35.2301   $35.23   $35.25   $35.20  
  Purchase #5 $126.84   6.470%   $135.0465   $135.05   $135.05   $135.00  
  Purchase #6 $169.88   8.217%   $183.839   $183.84   $183.85   $183.80  
  Purchase #7 $247.40   11.404%   $275.6135   $275.61   $275.60   $275.60  
  7 purchase totals = $1,096.09       $1,192.3614   $1,192.36   $1,192.40   $1,192.30