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 $221.80   11.283%   $246.8257   $246.83   $246.85   $246.80  
  Purchase #2 $210.57   6.837%   $224.9667   $224.97   $224.95   $225.00  
  Purchase #3 $187.85   4.525%   $196.3502   $196.35   $196.35   $196.40  
  Purchase #4 $29.63   4.205%   $30.8759   $30.88   $30.90   $30.90  
  Purchase #5 $55.95   10.107%   $61.6049   $61.60   $61.60   $61.60  
  Purchase #6 $115.57   6.654%   $123.26   $123.26   $123.25   $123.30  
  Purchase #7 $177.93   7.440%   $191.168   $191.17   $191.15   $191.20  
  7 purchase totals = $999.30       $1,075.0514   $1,075.06   $1,075.05   $1,075.20