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 $96.69   5.782%   $102.2806   $102.28   $102.30   $102.30  
  Purchase #2 $190.76   8.847%   $207.6365   $207.64   $207.65   $207.60  
  Purchase #3 $231.52   7.655%   $249.2429   $249.24   $249.25   $249.20  
  Purchase #4 $184.38   6.167%   $195.7507   $195.75   $195.75   $195.80  
  Purchase #5 $68.41   13.550%   $77.6796   $77.68   $77.70   $77.70  
  Purchase #6 $155.75   12.776%   $175.6486   $175.65   $175.65   $175.60  
  Purchase #7 $187.99   3.808%   $195.1487   $195.15   $195.15   $195.10  
  7 purchase totals = $1,115.50       $1,203.3876   $1,203.39   $1,203.45   $1,203.30