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 $117.34   10.736%   $129.9376   $129.94   $129.95   $129.90  
  Purchase #2 $176.36   11.159%   $196.04   $196.04   $196.05   $196.00  
  Purchase #3 $54.76   8.494%   $59.4113   $59.41   $59.40   $59.40  
  Purchase #4 $163.31   3.813%   $169.537   $169.54   $169.55   $169.50  
  Purchase #5 $150.64   4.552%   $157.4971   $157.50   $157.50   $157.50  
  Purchase #6 $70.39   5.618%   $74.3445   $74.34   $74.35   $74.30  
  Purchase #7 $157.32   7.611%   $169.2936   $169.29   $169.30   $169.30  
  7 purchase totals = $890.12       $956.0611   $956.06   $956.10   $955.90