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 $206.77   8.681%   $224.7197   $224.72   $224.70   $224.70  
  Purchase #2 $5.64   9.148%   $6.1559   $6.16   $6.15   $6.20  
  Purchase #3 $159.39   9.484%   $174.5065   $174.51   $174.50   $174.50  
  Purchase #4 $106.53   11.389%   $118.6627   $118.66   $118.65   $118.70  
  Purchase #5 $95.83   11.116%   $106.4825   $106.48   $106.50   $106.50  
  Purchase #6 $165.32   13.607%   $187.8151   $187.82   $187.80   $187.80  
  Purchase #7 $174.43   9.800%   $191.5241   $191.52   $191.50   $191.50  
  7 purchase totals = $913.91       $1,009.8665   $1,009.87   $1,009.80   $1,009.90