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 $197.75   3.171%   $204.0207   $204.02   $204.00   $204.00  
  Purchase #2 $180.71   6.702%   $192.8212   $192.82   $192.80   $192.80  
  Purchase #3 $59.37   11.163%   $65.9975   $66.00   $66.00   $66.00  
  Purchase #4 $122.83   8.331%   $133.063   $133.06   $133.05   $133.10  
  Purchase #5 $56.90   6.701%   $60.7129   $60.71   $60.70   $60.70  
  Purchase #6 $93.78   8.804%   $102.0364   $102.04   $102.05   $102.00  
  Purchase #7 $160.32   13.720%   $182.3159   $182.32   $182.30   $182.30  
  7 purchase totals = $871.66       $940.9676   $940.97   $940.90   $940.90