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 $33.32   6.526%   $35.4945   $35.49   $35.50   $35.50  
  Purchase #2 $192.64   6.394%   $204.9574   $204.96   $204.95   $205.00  
  Purchase #3 $80.89   5.618%   $85.4344   $85.43   $85.45   $85.40  
  Purchase #4 $66.42   11.417%   $74.0032   $74.00   $74.00   $74.00  
  Purchase #5 $195.49   3.855%   $203.0261   $203.03   $203.05   $203.00  
  Purchase #6 $176.28   10.256%   $194.3593   $194.36   $194.35   $194.40  
  Purchase #7 $85.96   9.140%   $93.8167   $93.82   $93.80   $93.80  
  7 purchase totals = $831.00       $891.0916   $891.09   $891.10   $891.10