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 $234.75   12.783%   $264.7581   $264.76   $264.75   $264.80  
  Purchase #2 $51.79   8.231%   $56.0528   $56.05   $56.05   $56.10  
  Purchase #3 $118.71   13.616%   $134.8736   $134.87   $134.85   $134.90  
  Purchase #4 $174.78   8.528%   $189.6852   $189.69   $189.70   $189.70  
  Purchase #5 $73.77   13.857%   $83.9923   $83.99   $84.00   $84.00  
  Purchase #6 $148.63   6.493%   $158.2805   $158.28   $158.30   $158.30  
  Purchase #7 $153.30   7.231%   $164.3851   $164.39   $164.40   $164.40  
  7 purchase totals = $955.73       $1,052.0276   $1,052.03   $1,052.05   $1,052.20