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 $237.97   3.716%   $246.813   $246.81   $246.80   $246.80  
  Purchase #2 $91.75   5.448%   $96.7485   $96.75   $96.75   $96.70  
  Purchase #3 $147.39   6.391%   $156.8097   $156.81   $156.80   $156.80  
  Purchase #4 $40.63   12.429%   $45.6799   $45.68   $45.70   $45.70  
  Purchase #5 $204.52   8.697%   $222.3071   $222.31   $222.30   $222.30  
  Purchase #6 $154.64   3.539%   $160.1127   $160.11   $160.10   $160.10  
  Purchase #7 $248.88   13.104%   $281.4932   $281.49   $281.50   $281.50  
  7 purchase totals = $1,125.78       $1,209.9641   $1,209.96   $1,209.95   $1,209.90