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 $214.43   8.553%   $232.7702   $232.77   $232.75   $232.80  
  Purchase #2 $78.87   9.458%   $86.3295   $86.33   $86.35   $86.30  
  Purchase #3 $99.95   10.172%   $110.1169   $110.12   $110.10   $110.10  
  Purchase #4 $191.39   7.677%   $206.083   $206.08   $206.10   $206.10  
  Purchase #5 $199.28   13.709%   $226.5993   $226.60   $226.60   $226.60  
  Purchase #6 $95.94   13.374%   $108.771   $108.77   $108.75   $108.80  
  Purchase #7 $162.25   5.103%   $170.5296   $170.53   $170.55   $170.50  
  7 purchase totals = $1,042.11       $1,141.1995   $1,141.20   $1,141.20   $1,141.20