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 $59.57   5.736%   $62.9869   $62.99   $63.00   $63.00  
  Purchase #2 $238.68   8.511%   $258.9941   $258.99   $259.00   $259.00  
  Purchase #3 $222.26   11.313%   $247.4043   $247.40   $247.40   $247.40  
  Purchase #4 $115.71   7.452%   $124.3327   $124.33   $124.35   $124.30  
  Purchase #5 $214.82   9.129%   $234.4309   $234.43   $234.45   $234.40  
  Purchase #6 $57.45   7.391%   $61.6961   $61.70   $61.70   $61.70  
  Purchase #7 $64.66   11.384%   $72.0209   $72.02   $72.00   $72.00  
  7 purchase totals = $973.15       $1,061.8659   $1,061.86   $1,061.90   $1,061.80