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 $32.57   6.153%   $34.574   $34.57   $34.55   $34.60  
  Purchase #2 $36.52   11.436%   $40.6964   $40.70   $40.70   $40.70  
  Purchase #3 $108.54   8.163%   $117.4001   $117.40   $117.40   $117.40  
  Purchase #4 $238.53   12.341%   $267.967   $267.97   $267.95   $268.00  
  Purchase #5 $218.28   6.843%   $233.2169   $233.22   $233.20   $233.20  
  Purchase #6 $199.36   6.187%   $211.6944   $211.69   $211.70   $211.70  
  Purchase #7 $208.38   12.737%   $234.9214   $234.92   $234.90   $234.90  
  7 purchase totals = $1,042.18       $1,140.4702   $1,140.47   $1,140.40   $1,140.50