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 $36.77   12.772%   $41.4663   $41.47   $41.45   $41.50  
  Purchase #2 $182.90   4.676%   $191.4524   $191.45   $191.45   $191.50  
  Purchase #3 $167.42   3.825%   $173.8238   $173.82   $173.80   $173.80  
  Purchase #4 $26.43   3.506%   $27.3566   $27.36   $27.35   $27.40  
  Purchase #5 $81.67   13.855%   $92.9854   $92.99   $93.00   $93.00  
  Purchase #6 $11.34   6.223%   $12.0457   $12.05   $12.05   $12.00  
  Purchase #7 $168.56   12.334%   $189.3502   $189.35   $189.35   $189.40  
  7 purchase totals = $675.09       $728.4804   $728.49   $728.45   $728.60