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 $61.77   12.178%   $69.2924   $69.29   $69.30   $69.30  
  Purchase #2 $67.95   6.590%   $72.4279   $72.43   $72.45   $72.40  
  Purchase #3 $161.62   3.429%   $167.1619   $167.16   $167.15   $167.20  
  Purchase #4 $188.86   8.325%   $204.5826   $204.58   $204.60   $204.60  
  Purchase #5 $32.88   7.237%   $35.2595   $35.26   $35.25   $35.30  
  Purchase #6 $89.85   4.119%   $93.5509   $93.55   $93.55   $93.60  
  Purchase #7 $180.73   8.641%   $196.3469   $196.35   $196.35   $196.30  
  7 purchase totals = $783.66       $838.6221   $838.62   $838.65   $838.70