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 $236.54   13.306%   $268.014   $268.01   $268.00   $268.00  
  Purchase #2 $61.38   11.160%   $68.23   $68.23   $68.25   $68.20  
  Purchase #3 $227.63   5.705%   $240.6163   $240.62   $240.60   $240.60  
  Purchase #4 $127.76   6.315%   $135.828   $135.83   $135.85   $135.80  
  Purchase #5 $118.77   13.732%   $135.0795   $135.08   $135.10   $135.10  
  Purchase #6 $35.41   10.686%   $39.1939   $39.19   $39.20   $39.20  
  Purchase #7 $180.26   11.544%   $201.0692   $201.07   $201.05   $201.10  
  7 purchase totals = $987.75       $1,088.0309   $1,088.03   $1,088.05   $1,088.00