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 $204.98   10.403%   $226.3041   $226.30   $226.30   $226.30  
  Purchase #2 $212.33   5.615%   $224.2523   $224.25   $224.25   $224.30  
  Purchase #3 $210.67   12.684%   $237.3914   $237.39   $237.40   $237.40  
  Purchase #4 $43.64   8.209%   $47.2224   $47.22   $47.20   $47.20  
  Purchase #5 $211.58   13.397%   $239.9254   $239.93   $239.95   $239.90  
  Purchase #6 $235.99   4.603%   $246.8526   $246.85   $246.85   $246.90  
  Purchase #7 $114.80   10.614%   $126.9849   $126.98   $127.00   $127.00  
  7 purchase totals = $1,233.99       $1,348.9331   $1,348.92   $1,348.95   $1,349.00