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 $173.93   6.343%   $184.9624   $184.96   $184.95   $185.00  
  Purchase #2 $151.93   7.236%   $162.9237   $162.92   $162.90   $162.90  
  Purchase #3 $210.84   5.381%   $222.1853   $222.19   $222.20   $222.20  
  Purchase #4 $41.39   9.747%   $45.4243   $45.42   $45.40   $45.40  
  Purchase #5 $205.97   9.803%   $226.1612   $226.16   $226.15   $226.20  
  Purchase #6 $106.37   5.655%   $112.3852   $112.39   $112.40   $112.40  
  Purchase #7 $83.99   7.376%   $90.1851   $90.19   $90.20   $90.20  
  7 purchase totals = $974.42       $1,044.2272   $1,044.23   $1,044.20   $1,044.30