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 $92.36   6.763%   $98.6063   $98.61   $98.60   $98.60  
  Purchase #2 $216.42   8.734%   $235.3221   $235.32   $235.30   $235.30  
  Purchase #3 $27.41   6.767%   $29.2648   $29.26   $29.25   $29.30  
  Purchase #4 $152.79   11.719%   $170.6955   $170.70   $170.70   $170.70  
  Purchase #5 $120.33   10.820%   $133.3497   $133.35   $133.35   $133.30  
  Purchase #6 $62.70   6.765%   $66.9417   $66.94   $66.95   $66.90  
  Purchase #7 $212.35   6.375%   $225.8873   $225.89   $225.90   $225.90  
  7 purchase totals = $884.36       $960.0674   $960.07   $960.05   $960.00