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 $195.31   8.829%   $212.5539   $212.55   $212.55   $212.60  
  Purchase #2 $101.89   4.589%   $106.5657   $106.57   $106.55   $106.60  
  Purchase #3 $247.34   11.759%   $276.4247   $276.42   $276.40   $276.40  
  Purchase #4 $173.73   10.557%   $192.0707   $192.07   $192.05   $192.10  
  Purchase #5 $22.92   6.267%   $24.3564   $24.36   $24.35   $24.40  
  Purchase #6 $87.90   9.747%   $96.4676   $96.47   $96.45   $96.50  
  Purchase #7 $133.56   13.176%   $151.1579   $151.16   $151.15   $151.20  
  7 purchase totals = $962.65       $1,059.5969   $1,059.60   $1,059.50   $1,059.80