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 $93.59   13.583%   $106.3023   $106.30   $106.30   $106.30  
  Purchase #2 $185.82   10.652%   $205.6135   $205.61   $205.60   $205.60  
  Purchase #3 $33.66   10.863%   $37.3165   $37.32   $37.30   $37.30  
  Purchase #4 $86.74   11.467%   $96.6865   $96.69   $96.70   $96.70  
  Purchase #5 $236.48   7.128%   $253.3363   $253.34   $253.35   $253.30  
  Purchase #6 $149.65   8.814%   $162.8402   $162.84   $162.85   $162.80  
  Purchase #7 $200.40   4.184%   $208.7847   $208.78   $208.80   $208.80  
  7 purchase totals = $986.34       $1,070.8800   $1,070.88   $1,070.90   $1,070.80