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 $23.84   5.844%   $25.2332   $25.23   $25.25   $25.20  
  Purchase #2 $184.37   5.461%   $194.4384   $194.44   $194.45   $194.40  
  Purchase #3 $44.92   11.396%   $50.0391   $50.04   $50.05   $50.00  
  Purchase #4 $45.31   7.656%   $48.7789   $48.78   $48.80   $48.80  
  Purchase #5 $208.65   3.298%   $215.5313   $215.53   $215.55   $215.50  
  Purchase #6 $60.88   9.839%   $66.87   $66.87   $66.85   $66.90  
  Purchase #7 $221.36   11.808%   $247.4982   $247.50   $247.50   $247.50  
  7 purchase totals = $789.33       $848.3891   $848.39   $848.45   $848.30