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 $217.27   10.349%   $239.7553   $239.76   $239.75   $239.80  
  Purchase #2 $226.27   11.178%   $251.5625   $251.56   $251.55   $251.60  
  Purchase #3 $82.83   11.793%   $92.5981   $92.60   $92.60   $92.60  
  Purchase #4 $100.32   5.204%   $105.5407   $105.54   $105.55   $105.50  
  Purchase #5 $225.60   7.539%   $242.608   $242.61   $242.60   $242.60  
  Purchase #6 $35.29   10.396%   $38.9587   $38.96   $38.95   $39.00  
  Purchase #7 $156.50   11.838%   $175.0265   $175.03   $175.05   $175.00  
  7 purchase totals = $1,044.08       $1,146.0498   $1,146.06   $1,146.05   $1,146.10