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 $69.41   11.776%   $77.5837   $77.58   $77.60   $77.60  
  Purchase #2 $82.71   9.799%   $90.8148   $90.81   $90.80   $90.80  
  Purchase #3 $113.50   9.265%   $124.0158   $124.02   $124.00   $124.00  
  Purchase #4 $196.74   4.363%   $205.3238   $205.32   $205.30   $205.30  
  Purchase #5 $32.86   7.221%   $35.2328   $35.23   $35.25   $35.20  
  Purchase #6 $153.62   13.525%   $174.3971   $174.40   $174.40   $174.40  
  Purchase #7 $164.34   6.427%   $174.9021   $174.90   $174.90   $174.90  
  7 purchase totals = $813.18       $882.2701   $882.26   $882.25   $882.20