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 $64.67   5.458%   $68.1997   $68.20   $68.20   $68.20  
  Purchase #2 $6.34   3.194%   $6.5425   $6.54   $6.55   $6.50  
  Purchase #3 $95.27   11.307%   $106.0422   $106.04   $106.05   $106.00  
  Purchase #4 $179.58   9.636%   $196.8843   $196.88   $196.90   $196.90  
  Purchase #5 $147.98   8.319%   $160.2905   $160.29   $160.30   $160.30  
  Purchase #6 $10.81   12.694%   $12.1822   $12.18   $12.20   $12.20  
  Purchase #7 $100.39   5.149%   $105.5591   $105.56   $105.55   $105.60  
  7 purchase totals = $605.04       $655.7005   $655.69   $655.75   $655.70