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 $64.33   13.698%   $73.1419   $73.14   $73.15   $73.10  
  Purchase #2 $244.62   12.394%   $274.9382   $274.94   $274.95   $274.90  
  Purchase #3 $52.42   3.477%   $54.2426   $54.24   $54.25   $54.20  
  Purchase #4 $241.28   13.835%   $274.6611   $274.66   $274.65   $274.70  
  Purchase #5 $14.47   5.493%   $15.2648   $15.26   $15.25   $15.30  
  Purchase #6 $172.40   10.599%   $190.6727   $190.67   $190.65   $190.70  
  Purchase #7 $203.25   8.640%   $220.8108   $220.81   $220.80   $220.80  
  7 purchase totals = $992.77       $1,103.7321   $1,103.72   $1,103.70   $1,103.70