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 $182.61   8.270%   $197.7118   $197.71   $197.70   $197.70  
  Purchase #2 $6.39   10.153%   $7.0388   $7.04   $7.05   $7.00  
  Purchase #3 $55.29   10.608%   $61.1552   $61.16   $61.15   $61.20  
  Purchase #4 $66.37   10.262%   $73.1809   $73.18   $73.20   $73.20  
  Purchase #5 $205.40   4.192%   $214.0104   $214.01   $214.00   $214.00  
  Purchase #6 $152.95   4.261%   $159.4672   $159.47   $159.45   $159.50  
  Purchase #7 $227.70   7.197%   $244.0876   $244.09   $244.10   $244.10  
  7 purchase totals = $896.71       $956.6519   $956.66   $956.65   $956.70