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 $211.85   12.825%   $239.0198   $239.02   $239.00   $239.00  
  Purchase #2 $188.83   9.424%   $206.6253   $206.63   $206.65   $206.60  
  Purchase #3 $243.66   6.414%   $259.2884   $259.29   $259.30   $259.30  
  Purchase #4 $88.98   4.258%   $92.7688   $92.77   $92.75   $92.80  
  Purchase #5 $139.52   8.388%   $151.2229   $151.22   $151.20   $151.20  
  Purchase #6 $160.71   7.585%   $172.8999   $172.90   $172.90   $172.90  
  Purchase #7 $86.28   8.618%   $93.7156   $93.72   $93.70   $93.70  
  7 purchase totals = $1,119.83       $1,215.5407   $1,215.55   $1,215.50   $1,215.50