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 $86.26   13.661%   $98.044   $98.04   $98.05   $98.00  
  Purchase #2 $32.92   9.701%   $36.1136   $36.11   $36.10   $36.10  
  Purchase #3 $66.51   5.555%   $70.2046   $70.20   $70.20   $70.20  
  Purchase #4 $232.43   5.616%   $245.4833   $245.48   $245.50   $245.50  
  Purchase #5 $9.56   8.168%   $10.3409   $10.34   $10.35   $10.30  
  Purchase #6 $187.47   8.167%   $202.7807   $202.78   $202.80   $202.80  
  Purchase #7 $62.45   6.327%   $66.4012   $66.40   $66.40   $66.40  
  7 purchase totals = $677.60       $729.3683   $729.35   $729.40   $729.30