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 $91.41   7.255%   $98.0418   $98.04   $98.05   $98.00  
  Purchase #2 $156.97   6.797%   $167.6393   $167.64   $167.65   $167.60  
  Purchase #3 $119.25   4.602%   $124.7379   $124.74   $124.75   $124.70  
  Purchase #4 $192.57   3.561%   $199.4274   $199.43   $199.45   $199.40  
  Purchase #5 $178.42   9.449%   $195.2789   $195.28   $195.30   $195.30  
  Purchase #6 $204.75   11.533%   $228.3638   $228.36   $228.35   $228.40  
  Purchase #7 $9.49   5.236%   $9.9869   $9.99   $10.00   $10.00  
  7 purchase totals = $952.86       $1,023.4760   $1,023.48   $1,023.55   $1,023.40