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 $43.96   8.662%   $47.7678   $47.77   $47.75   $47.80  
  Purchase #2 $55.54   9.187%   $60.6425   $60.64   $60.65   $60.60  
  Purchase #3 $227.65   8.572%   $247.1642   $247.16   $247.15   $247.20  
  Purchase #4 $207.77   7.795%   $223.9657   $223.97   $223.95   $224.00  
  Purchase #5 $135.32   10.475%   $149.4948   $149.49   $149.50   $149.50  
  Purchase #6 $207.40   4.314%   $216.3472   $216.35   $216.35   $216.30  
  Purchase #7 $105.71   8.566%   $114.7651   $114.77   $114.75   $114.80  
  7 purchase totals = $983.35       $1,060.1473   $1,060.15   $1,060.10   $1,060.20