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 $243.91   9.653%   $267.4546   $267.45   $267.45   $267.50  
  Purchase #2 $17.85   10.302%   $19.6889   $19.69   $19.70   $19.70  
  Purchase #3 $23.34   5.463%   $24.6151   $24.62   $24.60   $24.60  
  Purchase #4 $32.72   7.121%   $35.05   $35.05   $35.05   $35.10  
  Purchase #5 $67.98   12.407%   $76.4143   $76.41   $76.40   $76.40  
  Purchase #6 $21.70   13.709%   $24.6749   $24.67   $24.65   $24.70  
  Purchase #7 $47.63   11.121%   $52.9269   $52.93   $52.95   $52.90  
  7 purchase totals = $455.13       $500.8247   $500.82   $500.80   $500.90