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 $57.56   13.848%   $65.5309   $65.53   $65.55   $65.50  
  Purchase #2 $86.98   8.841%   $94.6699   $94.67   $94.65   $94.70  
  Purchase #3 $116.87   13.160%   $132.2501   $132.25   $132.25   $132.30  
  Purchase #4 $211.95   10.492%   $234.1878   $234.19   $234.20   $234.20  
  Purchase #5 $147.51   5.857%   $156.1497   $156.15   $156.15   $156.10  
  Purchase #6 $69.78   13.541%   $79.2289   $79.23   $79.25   $79.20  
  Purchase #7 $37.69   7.689%   $40.588   $40.59   $40.60   $40.60  
  7 purchase totals = $728.34       $802.6053   $802.61   $802.65   $802.60