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 $153.66   9.642%   $168.4759   $168.48   $168.50   $168.50  
  Purchase #2 $183.25   10.637%   $202.7423   $202.74   $202.75   $202.70  
  Purchase #3 $141.45   11.369%   $157.5315   $157.53   $157.55   $157.50  
  Purchase #4 $60.96   12.564%   $68.619   $68.62   $68.60   $68.60  
  Purchase #5 $100.78   10.118%   $110.9769   $110.98   $111.00   $111.00  
  Purchase #6 $211.73   8.354%   $229.4179   $229.42   $229.40   $229.40  
  Purchase #7 $54.45   4.202%   $56.738   $56.74   $56.75   $56.70  
  7 purchase totals = $906.28       $994.5015   $994.51   $994.55   $994.40