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 $59.95   12.451%   $67.4144   $67.41   $67.40   $67.40  
  Purchase #2 $109.63   13.802%   $124.7611   $124.76   $124.75   $124.80  
  Purchase #3 $247.82   7.369%   $266.0819   $266.08   $266.10   $266.10  
  Purchase #4 $226.95   7.484%   $243.9349   $243.93   $243.95   $243.90  
  Purchase #5 $81.26   3.648%   $84.2244   $84.22   $84.20   $84.20  
  Purchase #6 $160.98   8.106%   $174.029   $174.03   $174.05   $174.00  
  Purchase #7 $167.35   10.756%   $185.3502   $185.35   $185.35   $185.40  
  7 purchase totals = $1,053.94       $1,145.7959   $1,145.78   $1,145.80   $1,145.80