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 $248.37   11.471%   $276.8605   $276.86   $276.85   $276.90  
  Purchase #2 $165.93   3.462%   $171.6745   $171.67   $171.65   $171.70  
  Purchase #3 $155.65   4.314%   $162.3647   $162.36   $162.35   $162.40  
  Purchase #4 $104.93   13.658%   $119.2613   $119.26   $119.25   $119.30  
  Purchase #5 $229.72   13.136%   $259.896   $259.90   $259.90   $259.90  
  Purchase #6 $37.38   11.822%   $41.7991   $41.80   $41.80   $41.80  
  Purchase #7 $65.68   6.530%   $69.9689   $69.97   $69.95   $70.00  
  7 purchase totals = $1,007.66       $1,101.8250   $1,101.82   $1,101.75   $1,102.00