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 $38.44   12.567%   $43.2708   $43.27   $43.25   $43.30  
  Purchase #2 $229.91   7.228%   $246.5279   $246.53   $246.55   $246.50  
  Purchase #3 $207.85   7.300%   $223.0231   $223.02   $223.00   $223.00  
  Purchase #4 $153.78   9.285%   $168.0585   $168.06   $168.05   $168.10  
  Purchase #5 $51.96   3.212%   $53.629   $53.63   $53.65   $53.60  
  Purchase #6 $227.60   11.441%   $253.6397   $253.64   $253.65   $253.60  
  Purchase #7 $112.35   7.226%   $120.4684   $120.47   $120.45   $120.50  
  7 purchase totals = $1,021.89       $1,108.6174   $1,108.62   $1,108.60   $1,108.60