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 $241.96   13.756%   $275.244   $275.24   $275.25   $275.20  
  Purchase #2 $184.67   12.603%   $207.944   $207.94   $207.95   $207.90  
  Purchase #3 $249.88   8.644%   $271.4796   $271.48   $271.50   $271.50  
  Purchase #4 $74.81   11.788%   $83.6286   $83.63   $83.65   $83.60  
  Purchase #5 $113.91   10.649%   $126.0403   $126.04   $126.05   $126.00  
  Purchase #6 $98.75   10.711%   $109.3271   $109.33   $109.35   $109.30  
  Purchase #7 $119.85   10.204%   $132.0795   $132.08   $132.10   $132.10  
  7 purchase totals = $1,083.83       $1,205.7431   $1,205.74   $1,205.85   $1,205.60