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 $23.97   9.804%   $26.32   $26.32   $26.30   $26.30  
  Purchase #2 $220.75   3.735%   $228.995   $229.00   $229.00   $229.00  
  Purchase #3 $176.93   5.656%   $186.9372   $186.94   $186.95   $186.90  
  Purchase #4 $160.65   3.569%   $166.3836   $166.38   $166.40   $166.40  
  Purchase #5 $234.83   8.112%   $253.8794   $253.88   $253.90   $253.90  
  Purchase #6 $163.99   5.485%   $172.9849   $172.98   $173.00   $173.00  
  Purchase #7 $24.66   4.805%   $25.8449   $25.84   $25.85   $25.80  
  7 purchase totals = $1,005.78       $1,061.3450   $1,061.34   $1,061.40   $1,061.30