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 $182.72   6.228%   $194.0998   $194.10   $194.10   $194.10  
  Purchase #2 $10.90   6.671%   $11.6271   $11.63   $11.65   $11.60  
  Purchase #3 $250.32   7.190%   $268.318   $268.32   $268.30   $268.30  
  Purchase #4 $96.89   7.572%   $104.2265   $104.23   $104.25   $104.20  
  Purchase #5 $117.85   10.610%   $130.3539   $130.35   $130.35   $130.40  
  Purchase #6 $206.91   11.469%   $230.6405   $230.64   $230.65   $230.60  
  Purchase #7 $92.73   4.688%   $97.0772   $97.08   $97.10   $97.10  
  7 purchase totals = $958.32       $1,036.3430   $1,036.35   $1,036.40   $1,036.30