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 $247.47   11.805%   $276.6838   $276.68   $276.70   $276.70  
  Purchase #2 $91.30   9.111%   $99.6183   $99.62   $99.60   $99.60  
  Purchase #3 $60.38   10.462%   $66.697   $66.70   $66.70   $66.70  
  Purchase #4 $53.54   12.483%   $60.2234   $60.22   $60.20   $60.20  
  Purchase #5 $173.25   11.658%   $193.4475   $193.45   $193.45   $193.40  
  Purchase #6 $169.49   13.450%   $192.2864   $192.29   $192.30   $192.30  
  Purchase #7 $66.79   6.603%   $71.2001   $71.20   $71.20   $71.20  
  7 purchase totals = $862.22       $960.1565   $960.16   $960.15   $960.10