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 $246.77   6.239%   $262.166   $262.17   $262.15   $262.20  
  Purchase #2 $40.98   7.482%   $44.0461   $44.05   $44.05   $44.00  
  Purchase #3 $220.78   12.186%   $247.6843   $247.68   $247.70   $247.70  
  Purchase #4 $134.64   6.384%   $143.2354   $143.24   $143.25   $143.20  
  Purchase #5 $6.48   5.823%   $6.8573   $6.86   $6.85   $6.90  
  Purchase #6 $166.54   4.423%   $173.9061   $173.91   $173.90   $173.90  
  Purchase #7 $224.83   8.385%   $243.682   $243.68   $243.70   $243.70  
  7 purchase totals = $1,041.02       $1,121.5772   $1,121.59   $1,121.60   $1,121.60