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 $221.27   9.758%   $242.8615   $242.86   $242.85   $242.90  
  Purchase #2 $86.29   10.311%   $95.1874   $95.19   $95.20   $95.20  
  Purchase #3 $38.76   10.491%   $42.8263   $42.83   $42.85   $42.80  
  Purchase #4 $207.44   9.315%   $226.763   $226.76   $226.75   $226.80  
  Purchase #5 $6.27   6.701%   $6.6902   $6.69   $6.70   $6.70  
  Purchase #6 $244.96   11.867%   $274.0294   $274.03   $274.05   $274.00  
  Purchase #7 $242.29   12.355%   $272.2249   $272.22   $272.20   $272.20  
  7 purchase totals = $1,047.28       $1,160.5827   $1,160.58   $1,160.60   $1,160.60