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 $168.55   8.554%   $182.9678   $182.97   $182.95   $183.00  
  Purchase #2 $143.61   6.748%   $153.3008   $153.30   $153.30   $153.30  
  Purchase #3 $87.80   3.193%   $90.6035   $90.60   $90.60   $90.60  
  Purchase #4 $61.35   5.586%   $64.777   $64.78   $64.80   $64.80  
  Purchase #5 $132.93   5.404%   $140.1135   $140.11   $140.10   $140.10  
  Purchase #6 $215.89   7.464%   $232.004   $232.00   $232.00   $232.00  
  Purchase #7 $232.58   7.261%   $249.4676   $249.47   $249.45   $249.50  
  7 purchase totals = $1,042.71       $1,113.2342   $1,113.23   $1,113.20   $1,113.30