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 $44.78   3.378%   $46.2927   $46.29   $46.30   $46.30  
  Purchase #2 $243.30   7.571%   $261.7202   $261.72   $261.70   $261.70  
  Purchase #3 $103.77   13.358%   $117.6316   $117.63   $117.65   $117.60  
  Purchase #4 $76.87   3.718%   $79.728   $79.73   $79.75   $79.70  
  Purchase #5 $225.75   9.239%   $246.607   $246.61   $246.60   $246.60  
  Purchase #6 $90.62   9.784%   $99.4863   $99.49   $99.50   $99.50  
  Purchase #7 $173.45   3.190%   $178.9831   $178.98   $179.00   $179.00  
  7 purchase totals = $958.54       $1,030.4489   $1,030.45   $1,030.50   $1,030.40