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 $24.42   11.603%   $27.2535   $27.25   $27.25   $27.30  
  Purchase #2 $192.60   11.372%   $214.5025   $214.50   $214.50   $214.50  
  Purchase #3 $132.51   11.113%   $147.2358   $147.24   $147.25   $147.20  
  Purchase #4 $112.64   5.550%   $118.8915   $118.89   $118.90   $118.90  
  Purchase #5 $60.92   3.840%   $63.2593   $63.26   $63.25   $63.30  
  Purchase #6 $247.98   6.684%   $264.555   $264.56   $264.55   $264.60  
  Purchase #7 $127.52   6.593%   $135.9274   $135.93   $135.95   $135.90  
  7 purchase totals = $898.59       $971.6250   $971.63   $971.65   $971.70