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 $199.76   8.229%   $216.1983   $216.20   $216.20   $216.20  
  Purchase #2 $21.77   13.744%   $24.7621   $24.76   $24.75   $24.80  
  Purchase #3 $248.47   12.301%   $279.0343   $279.03   $279.05   $279.00  
  Purchase #4 $38.29   3.313%   $39.5585   $39.56   $39.55   $39.60  
  Purchase #5 $239.69   3.128%   $247.1875   $247.19   $247.20   $247.20  
  Purchase #6 $81.68   10.776%   $90.4818   $90.48   $90.50   $90.50  
  Purchase #7 $130.46   10.303%   $143.9013   $143.90   $143.90   $143.90  
  7 purchase totals = $960.12       $1,041.1238   $1,041.12   $1,041.15   $1,041.20