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 $59.43   13.196%   $67.2724   $67.27   $67.25   $67.30  
  Purchase #2 $87.47   11.123%   $97.1993   $97.20   $97.20   $97.20  
  Purchase #3 $204.95   12.697%   $230.9725   $230.97   $230.95   $231.00  
  Purchase #4 $33.89   10.472%   $37.439   $37.44   $37.45   $37.40  
  Purchase #5 $8.76   7.184%   $9.3893   $9.39   $9.40   $9.40  
  Purchase #6 $247.79   12.332%   $278.3475   $278.35   $278.35   $278.30  
  Purchase #7 $203.44   7.305%   $218.3013   $218.30   $218.30   $218.30  
  7 purchase totals = $845.73       $938.9213   $938.92   $938.90   $938.90