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 $55.84   8.279%   $60.463   $60.46   $60.45   $60.50  
  Purchase #2 $238.97   6.167%   $253.7073   $253.71   $253.70   $253.70  
  Purchase #3 $8.48   5.263%   $8.9263   $8.93   $8.95   $8.90  
  Purchase #4 $41.35   8.790%   $44.9847   $44.98   $45.00   $45.00  
  Purchase #5 $229.38   9.307%   $250.7284   $250.73   $250.75   $250.70  
  Purchase #6 $52.74   10.515%   $58.2856   $58.29   $58.30   $58.30  
  Purchase #7 $111.71   9.246%   $122.0387   $122.04   $122.05   $122.00  
  7 purchase totals = $738.47       $799.1340   $799.14   $799.20   $799.10