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 $212.65   11.302%   $236.6837   $236.68   $236.70   $236.70  
  Purchase #2 $116.42   10.171%   $128.2611   $128.26   $128.25   $128.30  
  Purchase #3 $121.60   12.176%   $136.406   $136.41   $136.40   $136.40  
  Purchase #4 $177.27   9.548%   $194.1957   $194.20   $194.20   $194.20  
  Purchase #5 $141.88   3.153%   $146.3535   $146.35   $146.35   $146.40  
  Purchase #6 $123.30   4.620%   $128.9965   $129.00   $129.00   $129.00  
  Purchase #7 $59.81   7.332%   $64.1953   $64.20   $64.20   $64.20  
  7 purchase totals = $952.93       $1,035.0918   $1,035.10   $1,035.10   $1,035.20