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 $242.52   9.254%   $264.9628   $264.96   $264.95   $265.00  
  Purchase #2 $113.35   5.298%   $119.3553   $119.36   $119.35   $119.40  
  Purchase #3 $147.91   6.608%   $157.6839   $157.68   $157.70   $157.70  
  Purchase #4 $239.31   9.611%   $262.3101   $262.31   $262.30   $262.30  
  Purchase #5 $40.73   11.444%   $45.3911   $45.39   $45.40   $45.40  
  Purchase #6 $77.42   7.659%   $83.3496   $83.35   $83.35   $83.30  
  Purchase #7 $27.93   3.371%   $28.8715   $28.87   $28.85   $28.90  
  7 purchase totals = $889.17       $961.9243   $961.92   $961.90   $962.00