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 $115.87   6.377%   $123.259   $123.26   $123.25   $123.30  
  Purchase #2 $6.91   9.649%   $7.5767   $7.58   $7.60   $7.60  
  Purchase #3 $187.67   4.288%   $195.7173   $195.72   $195.70   $195.70  
  Purchase #4 $200.26   6.589%   $213.4551   $213.46   $213.45   $213.50  
  Purchase #5 $6.34   10.426%   $7.001   $7.00   $7.00   $7.00  
  Purchase #6 $242.79   8.806%   $264.1701   $264.17   $264.15   $264.20  
  Purchase #7 $229.99   6.207%   $244.2655   $244.27   $244.25   $244.30  
  7 purchase totals = $989.83       $1,055.4447   $1,055.46   $1,055.40   $1,055.60