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 $238.41   7.344%   $255.9188   $255.92   $255.90   $255.90  
  Purchase #2 $59.25   5.183%   $62.3209   $62.32   $62.30   $62.30  
  Purchase #3 $71.89   8.454%   $77.9676   $77.97   $77.95   $78.00  
  Purchase #4 $189.52   6.313%   $201.4844   $201.48   $201.50   $201.50  
  Purchase #5 $63.55   4.292%   $66.2776   $66.28   $66.30   $66.30  
  Purchase #6 $73.66   3.384%   $76.1527   $76.15   $76.15   $76.20  
  Purchase #7 $155.47   8.137%   $168.1206   $168.12   $168.10   $168.10  
  7 purchase totals = $851.75       $908.2426   $908.24   $908.20   $908.30