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 $232.69   10.226%   $256.4849   $256.48   $256.50   $256.50  
  Purchase #2 $126.90   9.817%   $139.3578   $139.36   $139.35   $139.40  
  Purchase #3 $88.96   7.117%   $95.2913   $95.29   $95.30   $95.30  
  Purchase #4 $213.53   9.449%   $233.7064   $233.71   $233.70   $233.70  
  Purchase #5 $64.57   7.821%   $69.62   $69.62   $69.60   $69.60  
  Purchase #6 $61.25   10.475%   $67.6659   $67.67   $67.65   $67.70  
  Purchase #7 $118.63   12.575%   $133.5477   $133.55   $133.55   $133.50  
  7 purchase totals = $906.53       $995.6740   $995.68   $995.65   $995.70