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 $163.91   12.233%   $183.9611   $183.96   $183.95   $184.00  
  Purchase #2 $87.89   11.873%   $98.3252   $98.33   $98.35   $98.30  
  Purchase #3 $185.55   7.786%   $199.9969   $200.00   $200.00   $200.00  
  Purchase #4 $225.72   9.561%   $247.3011   $247.30   $247.30   $247.30  
  Purchase #5 $92.39   13.218%   $104.6021   $104.60   $104.60   $104.60  
  Purchase #6 $56.71   3.638%   $58.7731   $58.77   $58.75   $58.80  
  Purchase #7 $143.50   10.593%   $158.701   $158.70   $158.70   $158.70  
  7 purchase totals = $955.67       $1,051.6605   $1,051.66   $1,051.65   $1,051.70