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 $226.92   7.644%   $244.2658   $244.27   $244.25   $244.30  
  Purchase #2 $37.80   7.683%   $40.7042   $40.70   $40.70   $40.70  
  Purchase #3 $31.97   3.426%   $33.0653   $33.07   $33.05   $33.10  
  Purchase #4 $180.46   6.758%   $192.6555   $192.66   $192.65   $192.70  
  Purchase #5 $47.44   6.373%   $50.4634   $50.46   $50.45   $50.50  
  Purchase #6 $191.47   8.243%   $207.2529   $207.25   $207.25   $207.30  
  Purchase #7 $227.29   5.675%   $240.1887   $240.19   $240.20   $240.20  
  7 purchase totals = $943.35       $1,008.5958   $1,008.60   $1,008.55   $1,008.80