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 $65.91   8.284%   $71.37   $71.37   $71.35   $71.40  
  Purchase #2 $197.70   4.608%   $206.81   $206.81   $206.80   $206.80  
  Purchase #3 $211.80   3.712%   $219.662   $219.66   $219.65   $219.70  
  Purchase #4 $53.40   4.442%   $55.772   $55.77   $55.75   $55.80  
  Purchase #5 $92.95   5.836%   $98.3746   $98.37   $98.35   $98.40  
  Purchase #6 $237.28   6.212%   $252.0198   $252.02   $252.00   $252.00  
  Purchase #7 $26.77   12.479%   $30.1106   $30.11   $30.10   $30.10  
  7 purchase totals = $885.81       $934.1190   $934.11   $934.00   $934.20