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 $116.94   6.536%   $124.5832   $124.58   $124.60   $124.60  
  Purchase #2 $221.40   6.157%   $235.0316   $235.03   $235.05   $235.00  
  Purchase #3 $104.51   13.240%   $118.3471   $118.35   $118.35   $118.30  
  Purchase #4 $96.67   5.458%   $101.9462   $101.95   $101.95   $101.90  
  Purchase #5 $94.82   11.657%   $105.8732   $105.87   $105.85   $105.90  
  Purchase #6 $182.95   12.802%   $206.3713   $206.37   $206.35   $206.40  
  Purchase #7 $49.76   10.864%   $55.1659   $55.17   $55.15   $55.20  
  7 purchase totals = $867.05       $947.3185   $947.32   $947.30   $947.30