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 $231.66   12.532%   $260.6916   $260.69   $260.70   $260.70  
  Purchase #2 $213.31   13.264%   $241.6034   $241.60   $241.60   $241.60  
  Purchase #3 $63.30   13.165%   $71.6334   $71.63   $71.65   $71.60  
  Purchase #4 $6.83   3.423%   $7.0638   $7.06   $7.05   $7.10  
  Purchase #5 $120.86   6.133%   $128.2723   $128.27   $128.25   $128.30  
  Purchase #6 $108.89   6.157%   $115.5944   $115.59   $115.60   $115.60  
  Purchase #7 $205.43   7.186%   $220.1922   $220.19   $220.20   $220.20  
  7 purchase totals = $950.28       $1,045.0511   $1,045.03   $1,045.05   $1,045.10