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 $224.42   12.436%   $252.3289   $252.33   $252.35   $252.30  
  Purchase #2 $165.74   10.853%   $183.7278   $183.73   $183.75   $183.70  
  Purchase #3 $20.85   12.808%   $23.5205   $23.52   $23.50   $23.50  
  Purchase #4 $45.55   5.801%   $48.1924   $48.19   $48.20   $48.20  
  Purchase #5 $60.58   6.543%   $64.5437   $64.54   $64.55   $64.50  
  Purchase #6 $108.90   3.354%   $112.5525   $112.55   $112.55   $112.60  
  Purchase #7 $112.80   5.814%   $119.3582   $119.36   $119.35   $119.40  
  7 purchase totals = $738.84       $804.2240   $804.22   $804.25   $804.20