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 $46.93   3.669%   $48.6519   $48.65   $48.65   $48.70  
  Purchase #2 $131.97   8.146%   $142.7203   $142.72   $142.70   $142.70  
  Purchase #3 $195.29   5.241%   $205.5251   $205.53   $205.55   $205.50  
  Purchase #4 $225.70   8.755%   $245.46   $245.46   $245.45   $245.50  
  Purchase #5 $116.36   8.482%   $126.2297   $126.23   $126.25   $126.20  
  Purchase #6 $205.30   6.478%   $218.5993   $218.60   $218.60   $218.60  
  Purchase #7 $233.81   11.809%   $261.4206   $261.42   $261.40   $261.40  
  7 purchase totals = $1,155.36       $1,248.6069   $1,248.61   $1,248.60   $1,248.60