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 $92.59   7.559%   $99.5889   $99.59   $99.60   $99.60  
  Purchase #2 $126.65   9.752%   $139.0009   $139.00   $139.00   $139.00  
  Purchase #3 $103.43   12.440%   $116.2967   $116.30   $116.30   $116.30  
  Purchase #4 $123.26   7.497%   $132.5008   $132.50   $132.50   $132.50  
  Purchase #5 $55.95   4.368%   $58.3939   $58.39   $58.40   $58.40  
  Purchase #6 $204.94   3.644%   $212.408   $212.41   $212.40   $212.40  
  Purchase #7 $105.92   6.268%   $112.5591   $112.56   $112.55   $112.60  
  7 purchase totals = $812.74       $870.7483   $870.75   $870.75   $870.80