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 $109.94   3.461%   $113.745   $113.75   $113.75   $113.70  
  Purchase #2 $121.81   11.127%   $135.3638   $135.36   $135.35   $135.40  
  Purchase #3 $250.41   7.313%   $268.7225   $268.72   $268.70   $268.70  
  Purchase #4 $51.99   13.380%   $58.9463   $58.95   $58.95   $58.90  
  Purchase #5 $206.56   8.771%   $224.6774   $224.68   $224.70   $224.70  
  Purchase #6 $5.77   11.163%   $6.4141   $6.41   $6.40   $6.40  
  Purchase #7 $209.50   11.873%   $234.3739   $234.37   $234.35   $234.40  
  7 purchase totals = $955.98       $1,042.2430   $1,042.24   $1,042.20   $1,042.20