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 $180.61   13.673%   $205.3048   $205.30   $205.30   $205.30  
  Purchase #2 $141.65   8.489%   $153.6747   $153.67   $153.65   $153.70  
  Purchase #3 $246.51   8.685%   $267.9194   $267.92   $267.90   $267.90  
  Purchase #4 $173.53   9.815%   $190.562   $190.56   $190.55   $190.60  
  Purchase #5 $6.42   12.362%   $7.2136   $7.21   $7.20   $7.20  
  Purchase #6 $207.43   7.763%   $223.5328   $223.53   $223.55   $223.50  
  Purchase #7 $229.67   12.652%   $258.7278   $258.73   $258.75   $258.70  
  7 purchase totals = $1,185.82       $1,306.9351   $1,306.92   $1,306.90   $1,306.90