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 $244.74   8.757%   $266.1719   $266.17   $266.15   $266.20  
  Purchase #2 $224.86   3.591%   $232.9347   $232.93   $232.95   $232.90  
  Purchase #3 $239.73   10.121%   $263.9931   $263.99   $264.00   $264.00  
  Purchase #4 $219.82   3.844%   $228.2699   $228.27   $228.25   $228.30  
  Purchase #5 $92.96   9.549%   $101.8368   $101.84   $101.85   $101.80  
  Purchase #6 $91.90   10.459%   $101.5118   $101.51   $101.50   $101.50  
  Purchase #7 $163.82   6.684%   $174.7697   $174.77   $174.75   $174.80  
  7 purchase totals = $1,277.83       $1,369.4879   $1,369.48   $1,369.45   $1,369.50