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 $82.60   12.153%   $92.6384   $92.64   $92.65   $92.60  
  Purchase #2 $149.25   10.156%   $164.4078   $164.41   $164.40   $164.40  
  Purchase #3 $194.67   3.404%   $201.2966   $201.30   $201.30   $201.30  
  Purchase #4 $12.74   7.398%   $13.6825   $13.68   $13.70   $13.70  
  Purchase #5 $173.45   9.116%   $189.2617   $189.26   $189.25   $189.30  
  Purchase #6 $105.42   4.818%   $110.4991   $110.50   $110.50   $110.50  
  Purchase #7 $240.27   3.870%   $249.5684   $249.57   $249.55   $249.60  
  7 purchase totals = $958.40       $1,021.3545   $1,021.36   $1,021.35   $1,021.40