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 $117.92   5.693%   $124.6332   $124.63   $124.65   $124.60  
  Purchase #2 $120.79   4.592%   $126.3367   $126.34   $126.35   $126.30  
  Purchase #3 $107.35   11.872%   $120.0946   $120.09   $120.10   $120.10  
  Purchase #4 $34.62   7.641%   $37.2653   $37.27   $37.25   $37.30  
  Purchase #5 $115.75   5.315%   $121.9021   $121.90   $121.90   $121.90  
  Purchase #6 $132.45   4.674%   $138.6407   $138.64   $138.65   $138.60  
  Purchase #7 $160.49   4.776%   $168.155   $168.16   $168.15   $168.20  
  7 purchase totals = $789.37       $837.0276   $837.03   $837.05   $837.00