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 $61.35   5.748%   $64.8764   $64.88   $64.90   $64.90  
  Purchase #2 $120.60   4.812%   $126.4033   $126.40   $126.40   $126.40  
  Purchase #3 $229.88   6.595%   $245.0406   $245.04   $245.05   $245.00  
  Purchase #4 $73.58   8.428%   $79.7813   $79.78   $79.80   $79.80  
  Purchase #5 $16.92   8.562%   $18.3687   $18.37   $18.35   $18.40  
  Purchase #6 $166.85   10.181%   $183.837   $183.84   $183.85   $183.80  
  Purchase #7 $218.91   7.505%   $235.3392   $235.34   $235.35   $235.30  
  7 purchase totals = $888.09       $953.6465   $953.65   $953.70   $953.60