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 $32.92   9.131%   $35.9259   $35.93   $35.95   $35.90  
  Purchase #2 $234.97   7.597%   $252.8207   $252.82   $252.80   $252.80  
  Purchase #3 $109.28   12.832%   $123.3028   $123.30   $123.30   $123.30  
  Purchase #4 $159.80   10.759%   $176.9929   $176.99   $177.00   $177.00  
  Purchase #5 $166.32   3.194%   $171.6323   $171.63   $171.65   $171.60  
  Purchase #6 $92.37   12.617%   $104.0243   $104.02   $104.00   $104.00  
  Purchase #7 $186.26   8.587%   $202.2541   $202.25   $202.25   $202.30  
  7 purchase totals = $981.92       $1,066.9530   $1,066.94   $1,066.95   $1,066.90