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 $154.71   13.774%   $176.0198   $176.02   $176.00   $176.00  
  Purchase #2 $196.99   8.729%   $214.1853   $214.19   $214.20   $214.20  
  Purchase #3 $64.30   8.692%   $69.889   $69.89   $69.90   $69.90  
  Purchase #4 $30.74   11.323%   $34.2207   $34.22   $34.20   $34.20  
  Purchase #5 $147.77   9.242%   $161.4269   $161.43   $161.45   $161.40  
  Purchase #6 $126.66   7.797%   $136.5357   $136.54   $136.55   $136.50  
  Purchase #7 $161.28   8.191%   $174.4904   $174.49   $174.50   $174.50  
  7 purchase totals = $882.45       $966.7678   $966.78   $966.80   $966.70