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 $46.39   12.605%   $52.2375   $52.24   $52.25   $52.20  
  Purchase #2 $228.58   9.362%   $249.9797   $249.98   $250.00   $250.00  
  Purchase #3 $188.97   10.861%   $209.494   $209.49   $209.50   $209.50  
  Purchase #4 $238.97   13.747%   $271.8212   $271.82   $271.80   $271.80  
  Purchase #5 $44.35   7.640%   $47.7383   $47.74   $47.75   $47.70  
  Purchase #6 $150.42   7.112%   $161.1179   $161.12   $161.10   $161.10  
  Purchase #7 $175.76   9.239%   $191.9985   $192.00   $192.00   $192.00  
  7 purchase totals = $1,073.44       $1,184.3871   $1,184.39   $1,184.40   $1,184.30