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 $246.63   8.372%   $267.2779   $267.28   $267.30   $267.30  
  Purchase #2 $74.70   11.110%   $82.9992   $83.00   $83.00   $83.00  
  Purchase #3 $116.73   13.211%   $132.1512   $132.15   $132.15   $132.20  
  Purchase #4 $106.75   11.793%   $119.339   $119.34   $119.35   $119.30  
  Purchase #5 $183.66   12.730%   $207.0399   $207.04   $207.05   $207.00  
  Purchase #6 $172.39   4.697%   $180.4872   $180.49   $180.50   $180.50  
  Purchase #7 $16.80   5.200%   $17.6736   $17.67   $17.65   $17.70  
  7 purchase totals = $917.66       $1,006.9680   $1,006.97   $1,007.00   $1,007.00