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 $23.85   10.321%   $26.3116   $26.31   $26.30   $26.30  
  Purchase #2 $85.96   6.235%   $91.3196   $91.32   $91.30   $91.30  
  Purchase #3 $51.35   4.221%   $53.5175   $53.52   $53.50   $53.50  
  Purchase #4 $28.32   10.382%   $31.2602   $31.26   $31.25   $31.30  
  Purchase #5 $8.63   5.812%   $9.1316   $9.13   $9.15   $9.10  
  Purchase #6 $152.49   9.509%   $166.9903   $166.99   $167.00   $167.00  
  Purchase #7 $68.68   3.441%   $71.0433   $71.04   $71.05   $71.00  
  7 purchase totals = $419.28       $449.5741   $449.57   $449.55   $449.50