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 $217.53   8.371%   $235.7394   $235.74   $235.75   $235.70  
  Purchase #2 $244.96   10.661%   $271.0752   $271.08   $271.10   $271.10  
  Purchase #3 $141.30   10.149%   $155.6405   $155.64   $155.65   $155.60  
  Purchase #4 $194.85   9.762%   $213.8713   $213.87   $213.85   $213.90  
  Purchase #5 $194.57   6.527%   $207.2696   $207.27   $207.25   $207.30  
  Purchase #6 $141.36   6.673%   $150.793   $150.79   $150.80   $150.80  
  Purchase #7 $14.70   10.442%   $16.235   $16.24   $16.25   $16.20  
  7 purchase totals = $1,149.27       $1,250.6240   $1,250.63   $1,250.65   $1,250.60