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 $190.27   8.427%   $206.3041   $206.30   $206.30   $206.30  
  Purchase #2 $204.40   11.178%   $227.2478   $227.25   $227.25   $227.20  
  Purchase #3 $108.26   11.606%   $120.8247   $120.82   $120.80   $120.80  
  Purchase #4 $173.26   7.663%   $186.5369   $186.54   $186.55   $186.50  
  Purchase #5 $214.73   6.651%   $229.0117   $229.01   $229.00   $229.00  
  Purchase #6 $210.84   11.272%   $234.6059   $234.61   $234.60   $234.60  
  Purchase #7 $44.89   9.446%   $49.1303   $49.13   $49.15   $49.10  
  7 purchase totals = $1,146.65       $1,253.6614   $1,253.66   $1,253.65   $1,253.50