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 $48.51   13.342%   $54.9822   $54.98   $55.00   $55.00  
  Purchase #2 $17.70   8.689%   $19.238   $19.24   $19.25   $19.20  
  Purchase #3 $120.77   4.859%   $126.6382   $126.64   $126.65   $126.60  
  Purchase #4 $158.27   13.518%   $179.6649   $179.66   $179.65   $179.70  
  Purchase #5 $199.30   10.577%   $220.38   $220.38   $220.40   $220.40  
  Purchase #6 $118.70   9.333%   $129.7783   $129.78   $129.80   $129.80  
  Purchase #7 $191.56   13.410%   $217.2482   $217.25   $217.25   $217.20  
  7 purchase totals = $854.81       $947.9298   $947.93   $948.00   $947.90