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 $44.60   8.668%   $48.4659   $48.47   $48.45   $48.50  
  Purchase #2 $177.97   13.122%   $201.3232   $201.32   $201.30   $201.30  
  Purchase #3 $243.92   4.589%   $255.1135   $255.11   $255.10   $255.10  
  Purchase #4 $215.39   11.846%   $240.9051   $240.91   $240.90   $240.90  
  Purchase #5 $112.75   3.379%   $116.5598   $116.56   $116.55   $116.60  
  Purchase #6 $156.34   4.376%   $163.1814   $163.18   $163.20   $163.20  
  Purchase #7 $220.38   5.845%   $233.2612   $233.26   $233.25   $233.30  
  7 purchase totals = $1,171.35       $1,258.8101   $1,258.81   $1,258.75   $1,258.90