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 $244.80   7.164%   $262.3375   $262.34   $262.35   $262.30  
  Purchase #2 $66.37   10.121%   $73.0873   $73.09   $73.10   $73.10  
  Purchase #3 $63.28   5.634%   $66.8452   $66.85   $66.85   $66.80  
  Purchase #4 $24.58   5.429%   $25.9144   $25.91   $25.90   $25.90  
  Purchase #5 $117.92   3.190%   $121.6816   $121.68   $121.70   $121.70  
  Purchase #6 $230.39   9.421%   $252.095   $252.10   $252.10   $252.10  
  Purchase #7 $71.25   4.278%   $74.2981   $74.30   $74.30   $74.30  
  7 purchase totals = $818.59       $876.2591   $876.27   $876.30   $876.20