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 $236.73   12.482%   $266.2786   $266.28   $266.30   $266.30  
  Purchase #2 $108.30   3.377%   $111.9573   $111.96   $111.95   $112.00  
  Purchase #3 $86.55   12.528%   $97.393   $97.39   $97.40   $97.40  
  Purchase #4 $127.76   12.647%   $143.9178   $143.92   $143.90   $143.90  
  Purchase #5 $240.91   10.564%   $266.3597   $266.36   $266.35   $266.40  
  Purchase #6 $220.98   13.838%   $251.5592   $251.56   $251.55   $251.60  
  Purchase #7 $52.31   6.295%   $55.6029   $55.60   $55.60   $55.60  
  7 purchase totals = $1,073.54       $1,193.0685   $1,193.07   $1,193.05   $1,193.20