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 $207.64   8.832%   $225.9788   $225.98   $226.00   $226.00  
  Purchase #2 $137.89   3.399%   $142.5769   $142.58   $142.60   $142.60  
  Purchase #3 $15.36   13.637%   $17.4546   $17.45   $17.45   $17.50  
  Purchase #4 $40.85   13.234%   $46.2561   $46.26   $46.25   $46.30  
  Purchase #5 $246.64   9.121%   $269.136   $269.14   $269.15   $269.10  
  Purchase #6 $138.58   5.507%   $146.2116   $146.21   $146.20   $146.20  
  Purchase #7 $140.27   13.156%   $158.7239   $158.72   $158.70   $158.70  
  7 purchase totals = $927.23       $1,006.3379   $1,006.34   $1,006.35   $1,006.40