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 $47.80   12.161%   $53.613   $53.61   $53.60   $53.60  
  Purchase #2 $169.41   12.728%   $190.9725   $190.97   $190.95   $191.00  
  Purchase #3 $190.39   8.355%   $206.2971   $206.30   $206.30   $206.30  
  Purchase #4 $94.98   7.153%   $101.7739   $101.77   $101.75   $101.80  
  Purchase #5 $113.58   11.702%   $126.8711   $126.87   $126.85   $126.90  
  Purchase #6 $221.42   11.732%   $247.397   $247.40   $247.40   $247.40  
  Purchase #7 $184.99   10.664%   $204.7173   $204.72   $204.70   $204.70  
  7 purchase totals = $1,022.57       $1,131.6419   $1,131.64   $1,131.55   $1,131.70