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 $181.56   12.749%   $204.7071   $204.71   $204.70   $204.70  
  Purchase #2 $173.39   13.617%   $197.0005   $197.00   $197.00   $197.00  
  Purchase #3 $17.26   5.139%   $18.147   $18.15   $18.15   $18.10  
  Purchase #4 $34.78   7.584%   $37.4177   $37.42   $37.40   $37.40  
  Purchase #5 $204.76   13.395%   $232.1876   $232.19   $232.20   $232.20  
  Purchase #6 $249.43   7.829%   $268.9579   $268.96   $268.95   $269.00  
  Purchase #7 $135.51   13.375%   $153.6345   $153.63   $153.65   $153.60  
  7 purchase totals = $996.69       $1,112.0523   $1,112.06   $1,112.05   $1,112.00