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 $112.44   4.207%   $117.1704   $117.17   $117.15   $117.20  
  Purchase #2 $58.60   5.107%   $61.5927   $61.59   $61.60   $61.60  
  Purchase #3 $212.45   12.715%   $239.463   $239.46   $239.45   $239.50  
  Purchase #4 $243.33   11.631%   $271.6317   $271.63   $271.65   $271.60  
  Purchase #5 $186.88   12.365%   $209.9877   $209.99   $210.00   $210.00  
  Purchase #6 $159.94   10.502%   $176.7369   $176.74   $176.75   $176.70  
  Purchase #7 $62.88   10.731%   $69.6277   $69.63   $69.65   $69.60  
  7 purchase totals = $1,036.52       $1,146.2101   $1,146.21   $1,146.25   $1,146.20