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 $147.65   9.555%   $161.758   $161.76   $161.75   $161.80  
  Purchase #2 $75.71   13.115%   $85.6394   $85.64   $85.65   $85.60  
  Purchase #3 $12.31   12.541%   $13.8538   $13.85   $13.85   $13.90  
  Purchase #4 $191.68   9.403%   $209.7037   $209.70   $209.70   $209.70  
  Purchase #5 $25.53   8.306%   $27.6505   $27.65   $27.65   $27.70  
  Purchase #6 $181.49   3.815%   $188.4138   $188.41   $188.40   $188.40  
  Purchase #7 $247.69   3.234%   $255.7003   $255.70   $255.70   $255.70  
  7 purchase totals = $882.06       $942.7195   $942.71   $942.70   $942.80