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 $239.93   9.658%   $263.1024   $263.10   $263.10   $263.10  
  Purchase #2 $64.71   11.664%   $72.2578   $72.26   $72.25   $72.30  
  Purchase #3 $221.87   8.620%   $240.9952   $241.00   $241.00   $241.00  
  Purchase #4 $22.91   4.413%   $23.921   $23.92   $23.90   $23.90  
  Purchase #5 $245.60   9.800%   $269.6688   $269.67   $269.65   $269.70  
  Purchase #6 $53.75   8.109%   $58.1086   $58.11   $58.10   $58.10  
  Purchase #7 $177.95   13.286%   $201.5924   $201.59   $201.60   $201.60  
  7 purchase totals = $1,026.72       $1,129.6462   $1,129.65   $1,129.60   $1,129.70