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 $44.73   5.592%   $47.2313   $47.23   $47.25   $47.20  
  Purchase #2 $76.37   9.490%   $83.6175   $83.62   $83.60   $83.60  
  Purchase #3 $213.96   3.619%   $221.7032   $221.70   $221.70   $221.70  
  Purchase #4 $95.67   12.712%   $107.8316   $107.83   $107.85   $107.80  
  Purchase #5 $244.40   6.538%   $260.3789   $260.38   $260.40   $260.40  
  Purchase #6 $230.95   12.405%   $259.5993   $259.60   $259.60   $259.60  
  Purchase #7 $35.36   5.194%   $37.1966   $37.20   $37.20   $37.20  
  7 purchase totals = $941.44       $1,017.5584   $1,017.56   $1,017.60   $1,017.50