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 $52.98   10.420%   $58.5005   $58.50   $58.50   $58.50  
  Purchase #2 $112.55   5.124%   $118.3171   $118.32   $118.30   $118.30  
  Purchase #3 $248.85   6.813%   $265.8042   $265.80   $265.80   $265.80  
  Purchase #4 $22.68   11.159%   $25.2109   $25.21   $25.20   $25.20  
  Purchase #5 $69.44   7.346%   $74.5411   $74.54   $74.55   $74.50  
  Purchase #6 $213.83   11.176%   $237.7276   $237.73   $237.75   $237.70  
  Purchase #7 $127.94   6.691%   $136.5005   $136.50   $136.50   $136.50  
  7 purchase totals = $848.27       $916.6019   $916.60   $916.60   $916.50