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 $239.71   10.749%   $265.4764   $265.48   $265.50   $265.50  
  Purchase #2 $52.66   7.161%   $56.431   $56.43   $56.45   $56.40  
  Purchase #3 $92.68   9.850%   $101.809   $101.81   $101.80   $101.80  
  Purchase #4 $101.50   4.609%   $106.1781   $106.18   $106.20   $106.20  
  Purchase #5 $22.38   8.768%   $24.3423   $24.34   $24.35   $24.30  
  Purchase #6 $239.74   13.363%   $271.7765   $271.78   $271.80   $271.80  
  Purchase #7 $188.52   5.135%   $198.2005   $198.20   $198.20   $198.20  
  7 purchase totals = $937.19       $1,024.2138   $1,024.22   $1,024.30   $1,024.20