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 $69.25   7.155%   $74.2048   $74.20   $74.20   $74.20  
  Purchase #2 $146.53   6.786%   $156.4735   $156.47   $156.45   $156.50  
  Purchase #3 $69.26   10.283%   $76.382   $76.38   $76.40   $76.40  
  Purchase #4 $228.38   9.551%   $250.1926   $250.19   $250.20   $250.20  
  Purchase #5 $96.70   7.438%   $103.8925   $103.89   $103.90   $103.90  
  Purchase #6 $145.87   13.442%   $165.4778   $165.48   $165.50   $165.50  
  Purchase #7 $74.92   6.545%   $79.8235   $79.82   $79.80   $79.80  
  7 purchase totals = $830.91       $906.4467   $906.43   $906.45   $906.50