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 $177.73   10.692%   $196.7329   $196.73   $196.75   $196.70  
  Purchase #2 $10.86   12.117%   $12.1759   $12.18   $12.20   $12.20  
  Purchase #3 $57.91   13.164%   $65.5333   $65.53   $65.55   $65.50  
  Purchase #4 $54.92   7.343%   $58.9528   $58.95   $58.95   $59.00  
  Purchase #5 $212.46   3.826%   $220.5887   $220.59   $220.60   $220.60  
  Purchase #6 $113.93   8.400%   $123.5001   $123.50   $123.50   $123.50  
  Purchase #7 $76.71   6.209%   $81.4729   $81.47   $81.45   $81.50  
  7 purchase totals = $704.52       $758.9566   $758.95   $759.00   $759.00