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 $97.26   6.509%   $103.5907   $103.59   $103.60   $103.60  
  Purchase #2 $160.89   10.189%   $177.2831   $177.28   $177.30   $177.30  
  Purchase #3 $120.74   7.286%   $129.5371   $129.54   $129.55   $129.50  
  Purchase #4 $250.31   5.828%   $264.8981   $264.90   $264.90   $264.90  
  Purchase #5 $180.26   4.740%   $188.8043   $188.80   $188.80   $188.80  
  Purchase #6 $136.61   6.359%   $145.297   $145.30   $145.30   $145.30  
  Purchase #7 $218.40   5.232%   $229.8267   $229.83   $229.85   $229.80  
  7 purchase totals = $1,164.47       $1,239.2370   $1,239.24   $1,239.30   $1,239.20