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 $91.37   13.401%   $103.6145   $103.61   $103.60   $103.60  
  Purchase #2 $244.66   5.232%   $257.4606   $257.46   $257.45   $257.50  
  Purchase #3 $60.31   6.496%   $64.2277   $64.23   $64.25   $64.20  
  Purchase #4 $31.84   6.547%   $33.9246   $33.92   $33.90   $33.90  
  Purchase #5 $5.86   10.847%   $6.4956   $6.50   $6.50   $6.50  
  Purchase #6 $224.85   7.344%   $241.363   $241.36   $241.35   $241.40  
  Purchase #7 $45.80   8.642%   $49.758   $49.76   $49.75   $49.80  
  7 purchase totals = $704.69       $756.8440   $756.84   $756.80   $756.90