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 $113.36   11.432%   $126.3193   $126.32   $126.30   $126.30  
  Purchase #2 $171.99   7.651%   $185.149   $185.15   $185.15   $185.10  
  Purchase #3 $63.38   5.807%   $67.0605   $67.06   $67.05   $67.10  
  Purchase #4 $141.26   5.198%   $148.6027   $148.60   $148.60   $148.60  
  Purchase #5 $86.59   12.286%   $97.2284   $97.23   $97.25   $97.20  
  Purchase #6 $94.83   9.160%   $103.5164   $103.52   $103.50   $103.50  
  Purchase #7 $235.25   3.533%   $243.5614   $243.56   $243.55   $243.60  
  7 purchase totals = $906.66       $971.4377   $971.44   $971.40   $971.40