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 $59.49   9.430%   $65.0999   $65.10   $65.10   $65.10  
  Purchase #2 $212.87   3.347%   $219.9948   $219.99   $220.00   $220.00  
  Purchase #3 $57.47   8.129%   $62.1417   $62.14   $62.15   $62.10  
  Purchase #4 $41.53   10.375%   $45.8387   $45.84   $45.85   $45.80  
  Purchase #5 $215.85   10.824%   $239.2136   $239.21   $239.20   $239.20  
  Purchase #6 $47.43   11.717%   $52.9874   $52.99   $53.00   $53.00  
  Purchase #7 $228.64   5.365%   $240.9065   $240.91   $240.90   $240.90  
  7 purchase totals = $863.28       $926.1826   $926.18   $926.20   $926.10