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 $205.28   13.822%   $233.6538   $233.65   $233.65   $233.70  
  Purchase #2 $166.81   9.449%   $182.5719   $182.57   $182.55   $182.60  
  Purchase #3 $95.28   11.239%   $105.9885   $105.99   $106.00   $106.00  
  Purchase #4 $44.62   13.604%   $50.6901   $50.69   $50.70   $50.70  
  Purchase #5 $231.94   3.515%   $240.0927   $240.09   $240.10   $240.10  
  Purchase #6 $91.66   6.750%   $97.8471   $97.85   $97.85   $97.80  
  Purchase #7 $221.41   8.612%   $240.4778   $240.48   $240.50   $240.50  
  7 purchase totals = $1,057.00       $1,151.3219   $1,151.32   $1,151.35   $1,151.40