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 $196.59   5.866%   $208.122   $208.12   $208.10   $208.10  
  Purchase #2 $246.99   9.718%   $270.9925   $270.99   $271.00   $271.00  
  Purchase #3 $165.95   11.257%   $184.631   $184.63   $184.65   $184.60  
  Purchase #4 $209.61   9.483%   $229.4873   $229.49   $229.50   $229.50  
  Purchase #5 $87.37   3.867%   $90.7486   $90.75   $90.75   $90.70  
  Purchase #6 $225.46   3.485%   $233.3173   $233.32   $233.30   $233.30  
  Purchase #7 $137.78   12.748%   $155.3442   $155.34   $155.35   $155.30  
  7 purchase totals = $1,269.75       $1,372.6429   $1,372.64   $1,372.65   $1,372.50