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 $196.31   11.597%   $219.0761   $219.08   $219.10   $219.10  
  Purchase #2 $125.87   10.331%   $138.8736   $138.87   $138.85   $138.90  
  Purchase #3 $68.85   13.747%   $78.3148   $78.31   $78.30   $78.30  
  Purchase #4 $236.28   13.674%   $268.5889   $268.59   $268.60   $268.60  
  Purchase #5 $138.25   5.373%   $145.6782   $145.68   $145.70   $145.70  
  Purchase #6 $54.27   6.708%   $57.9104   $57.91   $57.90   $57.90  
  Purchase #7 $78.76   11.385%   $87.7268   $87.73   $87.75   $87.70  
  7 purchase totals = $898.59       $996.1688   $996.17   $996.20   $996.20