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 $42.53   3.534%   $44.033   $44.03   $44.05   $44.00  
  Purchase #2 $227.83   9.262%   $248.9316   $248.93   $248.95   $248.90  
  Purchase #3 $139.84   11.113%   $155.3804   $155.38   $155.40   $155.40  
  Purchase #4 $207.58   9.454%   $227.2046   $227.20   $227.20   $227.20  
  Purchase #5 $228.36   13.674%   $259.5859   $259.59   $259.60   $259.60  
  Purchase #6 $127.37   6.151%   $135.2045   $135.20   $135.20   $135.20  
  Purchase #7 $151.64   12.349%   $170.366   $170.37   $170.35   $170.40  
  7 purchase totals = $1,125.15       $1,240.7060   $1,240.70   $1,240.75   $1,240.70