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 $237.58   9.664%   $260.5397   $260.54   $260.55   $260.50  
  Purchase #2 $120.26   11.668%   $134.2919   $134.29   $134.30   $134.30  
  Purchase #3 $213.46   3.601%   $221.1467   $221.15   $221.15   $221.10  
  Purchase #4 $60.85   6.240%   $64.647   $64.65   $64.65   $64.60  
  Purchase #5 $25.35   13.866%   $28.865   $28.87   $28.85   $28.90  
  Purchase #6 $60.93   11.325%   $67.8303   $67.83   $67.85   $67.80  
  Purchase #7 $183.60   5.275%   $193.2849   $193.28   $193.30   $193.30  
  7 purchase totals = $902.03       $970.6055   $970.61   $970.65   $970.50