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 $21.44   3.418%   $22.1728   $22.17   $22.15   $22.20  
  Purchase #2 $192.76   10.426%   $212.8572   $212.86   $212.85   $212.90  
  Purchase #3 $40.97   5.768%   $43.3331   $43.33   $43.35   $43.30  
  Purchase #4 $113.36   6.366%   $120.5765   $120.58   $120.60   $120.60  
  Purchase #5 $158.32   6.577%   $168.7327   $168.73   $168.75   $168.70  
  Purchase #6 $89.65   8.382%   $97.1645   $97.16   $97.15   $97.20  
  Purchase #7 $87.94   9.565%   $96.3515   $96.35   $96.35   $96.40  
  7 purchase totals = $704.44       $761.1883   $761.18   $761.20   $761.30