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 $249.87   9.567%   $273.7751   $273.78   $273.80   $273.80  
  Purchase #2 $58.57   12.179%   $65.7032   $65.70   $65.70   $65.70  
  Purchase #3 $62.76   4.544%   $65.6118   $65.61   $65.60   $65.60  
  Purchase #4 $71.83   10.366%   $79.2759   $79.28   $79.30   $79.30  
  Purchase #5 $84.70   4.356%   $88.3895   $88.39   $88.40   $88.40  
  Purchase #6 $206.82   4.642%   $216.4206   $216.42   $216.40   $216.40  
  Purchase #7 $120.63   5.173%   $126.8702   $126.87   $126.85   $126.90  
  7 purchase totals = $855.18       $916.0463   $916.05   $916.05   $916.10