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 $82.31   13.251%   $93.2169   $93.22   $93.20   $93.20  
  Purchase #2 $154.47   11.740%   $172.6048   $172.60   $172.60   $172.60  
  Purchase #3 $185.80   8.790%   $202.1318   $202.13   $202.15   $202.10  
  Purchase #4 $92.48   6.471%   $98.4644   $98.46   $98.45   $98.50  
  Purchase #5 $51.58   10.711%   $57.1047   $57.10   $57.10   $57.10  
  Purchase #6 $18.64   5.324%   $19.6324   $19.63   $19.65   $19.60  
  Purchase #7 $211.61   13.786%   $240.7826   $240.78   $240.80   $240.80  
  7 purchase totals = $796.89       $883.9376   $883.92   $883.95   $883.90