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 $96.69   8.798%   $105.1968   $105.20   $105.20   $105.20  
  Purchase #2 $196.39   3.439%   $203.1439   $203.14   $203.15   $203.10  
  Purchase #3 $243.92   13.141%   $275.9735   $275.97   $275.95   $276.00  
  Purchase #4 $147.56   9.427%   $161.4705   $161.47   $161.45   $161.50  
  Purchase #5 $246.73   13.765%   $280.6924   $280.69   $280.70   $280.70  
  Purchase #6 $19.47   10.627%   $21.5391   $21.54   $21.55   $21.50  
  Purchase #7 $180.46   6.561%   $192.3   $192.30   $192.30   $192.30  
  7 purchase totals = $1,131.22       $1,240.3162   $1,240.31   $1,240.30   $1,240.30