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 $141.56   5.713%   $149.6473   $149.65   $149.65   $149.60  
  Purchase #2 $158.57   3.199%   $163.6427   $163.64   $163.65   $163.60  
  Purchase #3 $68.76   11.535%   $76.6915   $76.69   $76.70   $76.70  
  Purchase #4 $226.98   4.570%   $237.353   $237.35   $237.35   $237.40  
  Purchase #5 $82.94   4.681%   $86.8224   $86.82   $86.80   $86.80  
  Purchase #6 $161.77   7.247%   $173.4935   $173.49   $173.50   $173.50  
  Purchase #7 $25.73   3.117%   $26.532   $26.53   $26.55   $26.50  
  7 purchase totals = $866.31       $914.1824   $914.17   $914.20   $914.10