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 $243.76   7.793%   $262.7562   $262.76   $262.75   $262.80  
  Purchase #2 $7.65   10.359%   $8.4425   $8.44   $8.45   $8.40  
  Purchase #3 $205.78   3.451%   $212.8815   $212.88   $212.90   $212.90  
  Purchase #4 $222.49   13.709%   $252.9912   $252.99   $253.00   $253.00  
  Purchase #5 $49.80   3.606%   $51.5958   $51.60   $51.60   $51.60  
  Purchase #6 $85.84   7.382%   $92.1767   $92.18   $92.20   $92.20  
  Purchase #7 $152.33   8.351%   $165.0511   $165.05   $165.05   $165.10  
  7 purchase totals = $967.65       $1,045.8950   $1,045.90   $1,045.95   $1,046.00