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 $162.46   10.469%   $179.4679   $179.47   $179.45   $179.50  
  Purchase #2 $243.66   5.734%   $257.6315   $257.63   $257.65   $257.60  
  Purchase #3 $227.58   10.596%   $251.6944   $251.69   $251.70   $251.70  
  Purchase #4 $61.79   10.107%   $68.0351   $68.04   $68.05   $68.00  
  Purchase #5 $164.49   8.590%   $178.6197   $178.62   $178.60   $178.60  
  Purchase #6 $101.41   5.177%   $106.66   $106.66   $106.65   $106.70  
  Purchase #7 $148.38   9.848%   $162.9925   $162.99   $163.00   $163.00  
  7 purchase totals = $1,109.77       $1,205.1011   $1,205.10   $1,205.10   $1,205.10