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 $113.87   8.640%   $123.7084   $123.71   $123.70   $123.70  
  Purchase #2 $5.70   5.642%   $6.0216   $6.02   $6.00   $6.00  
  Purchase #3 $245.70   6.252%   $261.0612   $261.06   $261.05   $261.10  
  Purchase #4 $167.72   9.254%   $183.2408   $183.24   $183.25   $183.20  
  Purchase #5 $64.84   3.369%   $67.0245   $67.02   $67.00   $67.00  
  Purchase #6 $245.25   8.648%   $266.4592   $266.46   $266.45   $266.50  
  Purchase #7 $39.72   10.759%   $43.9935   $43.99   $44.00   $44.00  
  7 purchase totals = $882.80       $951.5092   $951.50   $951.45   $951.50