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 $208.27   11.506%   $232.2335   $232.23   $232.25   $232.20  
  Purchase #2 $25.41   3.708%   $26.3522   $26.35   $26.35   $26.40  
  Purchase #3 $97.54   9.173%   $106.4873   $106.49   $106.50   $106.50  
  Purchase #4 $87.90   10.814%   $97.4055   $97.41   $97.40   $97.40  
  Purchase #5 $235.26   6.391%   $250.2955   $250.30   $250.30   $250.30  
  Purchase #6 $109.44   6.523%   $116.5788   $116.58   $116.60   $116.60  
  Purchase #7 $46.55   9.266%   $50.8633   $50.86   $50.85   $50.90  
  7 purchase totals = $810.37       $880.2161   $880.22   $880.25   $880.30