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 $52.31   4.525%   $54.677   $54.68   $54.70   $54.70  
  Purchase #2 $125.71   5.251%   $132.311   $132.31   $132.30   $132.30  
  Purchase #3 $77.33   13.686%   $87.9134   $87.91   $87.90   $87.90  
  Purchase #4 $208.50   8.561%   $226.3497   $226.35   $226.35   $226.30  
  Purchase #5 $60.34   13.622%   $68.5595   $68.56   $68.55   $68.60  
  Purchase #6 $58.76   13.308%   $66.5798   $66.58   $66.60   $66.60  
  Purchase #7 $36.67   5.395%   $38.6483   $38.65   $38.65   $38.60  
  7 purchase totals = $619.62       $675.0387   $675.04   $675.05   $675.00