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 $222.89   7.519%   $239.6491   $239.65   $239.65   $239.60  
  Purchase #2 $150.39   11.265%   $167.3314   $167.33   $167.35   $167.30  
  Purchase #3 $249.91   11.249%   $278.0224   $278.02   $278.00   $278.00  
  Purchase #4 $139.57   10.761%   $154.5891   $154.59   $154.60   $154.60  
  Purchase #5 $210.53   5.207%   $221.4923   $221.49   $221.50   $221.50  
  Purchase #6 $210.56   3.387%   $217.6917   $217.69   $217.70   $217.70  
  Purchase #7 $160.74   3.311%   $166.0621   $166.06   $166.05   $166.10  
  7 purchase totals = $1,344.59       $1,444.8381   $1,444.83   $1,444.85   $1,444.80