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 $216.70   3.624%   $224.5532   $224.55   $224.55   $224.60  
  Purchase #2 $55.44   9.174%   $60.5261   $60.53   $60.55   $60.50  
  Purchase #3 $113.32   9.438%   $124.0151   $124.02   $124.00   $124.00  
  Purchase #4 $140.43   4.159%   $146.2705   $146.27   $146.25   $146.30  
  Purchase #5 $10.76   7.103%   $11.5243   $11.52   $11.50   $11.50  
  Purchase #6 $233.67   3.283%   $241.3414   $241.34   $241.35   $241.30  
  Purchase #7 $110.31   6.862%   $117.8795   $117.88   $117.90   $117.90  
  7 purchase totals = $880.63       $926.1101   $926.11   $926.10   $926.10