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 $239.69   12.507%   $269.668   $269.67   $269.65   $269.70  
  Purchase #2 $122.29   8.224%   $132.3471   $132.35   $132.35   $132.30  
  Purchase #3 $82.34   6.547%   $87.7308   $87.73   $87.75   $87.70  
  Purchase #4 $60.87   5.446%   $64.185   $64.19   $64.20   $64.20  
  Purchase #5 $6.80   12.502%   $7.6501   $7.65   $7.65   $7.70  
  Purchase #6 $152.94   10.823%   $169.4927   $169.49   $169.50   $169.50  
  Purchase #7 $119.32   5.841%   $126.2895   $126.29   $126.30   $126.30  
  7 purchase totals = $784.25       $857.3632   $857.37   $857.40   $857.40