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 $55.33   11.698%   $61.8025   $61.80   $61.80   $61.80  
  Purchase #2 $114.30   11.708%   $127.6822   $127.68   $127.70   $127.70  
  Purchase #3 $180.84   13.774%   $205.7489   $205.75   $205.75   $205.70  
  Purchase #4 $103.98   9.615%   $113.9777   $113.98   $114.00   $114.00  
  Purchase #5 $71.36   8.698%   $77.5669   $77.57   $77.55   $77.60  
  Purchase #6 $109.46   6.441%   $116.5103   $116.51   $116.50   $116.50  
  Purchase #7 $109.99   3.384%   $113.7121   $113.71   $113.70   $113.70  
  7 purchase totals = $745.26       $817.0006   $817.00   $817.00   $817.00