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 $172.78   12.869%   $195.0151   $195.02   $195.00   $195.00  
  Purchase #2 $30.39   3.193%   $31.3604   $31.36   $31.35   $31.40  
  Purchase #3 $170.35   6.118%   $180.772   $180.77   $180.75   $180.80  
  Purchase #4 $153.71   5.299%   $161.8551   $161.86   $161.85   $161.90  
  Purchase #5 $180.81   5.656%   $191.0366   $191.04   $191.05   $191.00  
  Purchase #6 $153.75   5.733%   $162.5645   $162.56   $162.55   $162.60  
  Purchase #7 $22.94   6.170%   $24.3554   $24.36   $24.35   $24.40  
  7 purchase totals = $884.73       $946.9591   $946.97   $946.90   $947.10