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 $188.70   8.783%   $205.2735   $205.27   $205.25   $205.30  
  Purchase #2 $162.26   8.194%   $175.5556   $175.56   $175.55   $175.60  
  Purchase #3 $82.93   3.858%   $86.1294   $86.13   $86.15   $86.10  
  Purchase #4 $106.87   5.856%   $113.1283   $113.13   $113.15   $113.10  
  Purchase #5 $162.92   6.425%   $173.3876   $173.39   $173.40   $173.40  
  Purchase #6 $116.96   4.757%   $122.5238   $122.52   $122.50   $122.50  
  Purchase #7 $125.93   10.342%   $138.9537   $138.95   $138.95   $139.00  
  7 purchase totals = $946.57       $1,014.9519   $1,014.95   $1,014.95   $1,015.00