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 $44.76   12.298%   $50.2646   $50.26   $50.25   $50.30  
  Purchase #2 $145.25   5.708%   $153.5409   $153.54   $153.55   $153.50  
  Purchase #3 $63.79   8.403%   $69.1503   $69.15   $69.15   $69.20  
  Purchase #4 $245.70   4.741%   $257.3486   $257.35   $257.35   $257.30  
  Purchase #5 $26.42   7.724%   $28.4607   $28.46   $28.45   $28.50  
  Purchase #6 $171.69   12.707%   $193.5066   $193.51   $193.50   $193.50  
  Purchase #7 $234.82   10.732%   $260.0209   $260.02   $260.00   $260.00  
  7 purchase totals = $932.43       $1,012.2926   $1,012.29   $1,012.25   $1,012.30