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 $247.61   5.828%   $262.0407   $262.04   $262.05   $262.00  
  Purchase #2 $211.46   8.253%   $228.9118   $228.91   $228.90   $228.90  
  Purchase #3 $130.42   10.141%   $143.6459   $143.65   $143.65   $143.60  
  Purchase #4 $23.89   4.368%   $24.9335   $24.93   $24.95   $24.90  
  Purchase #5 $221.34   8.817%   $240.8555   $240.86   $240.85   $240.90  
  Purchase #6 $116.75   5.534%   $123.2109   $123.21   $123.20   $123.20  
  Purchase #7 $240.51   12.454%   $270.4631   $270.46   $270.45   $270.50  
  7 purchase totals = $1,191.98       $1,294.0614   $1,294.06   $1,294.05   $1,294.00