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 $99.70   13.139%   $112.7996   $112.80   $112.80   $112.80  
  Purchase #2 $222.75   7.337%   $239.0932   $239.09   $239.10   $239.10  
  Purchase #3 $201.45   13.131%   $227.9024   $227.90   $227.90   $227.90  
  Purchase #4 $171.43   4.498%   $179.1409   $179.14   $179.15   $179.10  
  Purchase #5 $215.25   6.414%   $229.0561   $229.06   $229.05   $229.10  
  Purchase #6 $57.74   11.316%   $64.2739   $64.27   $64.25   $64.30  
  Purchase #7 $226.54   5.350%   $238.6599   $238.66   $238.65   $238.70  
  7 purchase totals = $1,194.86       $1,290.9260   $1,290.92   $1,290.90   $1,291.00