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 $237.37   12.855%   $267.8839   $267.88   $267.90   $267.90  
  Purchase #2 $107.48   10.721%   $119.0029   $119.00   $119.00   $119.00  
  Purchase #3 $49.41   7.477%   $53.1044   $53.10   $53.10   $53.10  
  Purchase #4 $207.57   5.798%   $219.6049   $219.60   $219.60   $219.60  
  Purchase #5 $245.51   12.626%   $276.5081   $276.51   $276.50   $276.50  
  Purchase #6 $189.59   7.756%   $204.2946   $204.29   $204.30   $204.30  
  Purchase #7 $17.97   7.319%   $19.2852   $19.29   $19.30   $19.30  
  7 purchase totals = $1,054.90       $1,159.6840   $1,159.67   $1,159.70   $1,159.70