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 $41.93   5.155%   $44.0915   $44.09   $44.10   $44.10  
  Purchase #2 $58.73   5.779%   $62.124   $62.12   $62.10   $62.10  
  Purchase #3 $68.75   7.603%   $73.9771   $73.98   $74.00   $74.00  
  Purchase #4 $123.60   11.818%   $138.207   $138.21   $138.20   $138.20  
  Purchase #5 $174.42   9.184%   $190.4387   $190.44   $190.45   $190.40  
  Purchase #6 $63.44   13.341%   $71.9035   $71.90   $71.90   $71.90  
  Purchase #7 $10.36   13.616%   $11.7706   $11.77   $11.75   $11.80  
  7 purchase totals = $541.23       $592.5124   $592.51   $592.50   $592.50