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 $100.52   7.331%   $107.8891   $107.89   $107.90   $107.90  
  Purchase #2 $186.94   13.549%   $212.2685   $212.27   $212.25   $212.30  
  Purchase #3 $10.89   3.567%   $11.2784   $11.28   $11.30   $11.30  
  Purchase #4 $180.96   9.186%   $197.583   $197.58   $197.60   $197.60  
  Purchase #5 $214.83   4.577%   $224.6628   $224.66   $224.65   $224.70  
  Purchase #6 $129.90   11.421%   $144.7359   $144.74   $144.75   $144.70  
  Purchase #7 $227.61   13.636%   $258.6469   $258.65   $258.65   $258.60  
  7 purchase totals = $1,051.65       $1,157.0646   $1,157.07   $1,157.10   $1,157.10