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 $67.99   5.740%   $71.8926   $71.89   $71.90   $71.90  
  Purchase #2 $82.39   5.808%   $87.1752   $87.18   $87.20   $87.20  
  Purchase #3 $162.56   12.265%   $182.498   $182.50   $182.50   $182.50  
  Purchase #4 $183.76   12.783%   $207.25   $207.25   $207.25   $207.30  
  Purchase #5 $201.46   4.449%   $210.423   $210.42   $210.40   $210.40  
  Purchase #6 $199.55   6.622%   $212.7642   $212.76   $212.75   $212.80  
  Purchase #7 $87.86   13.439%   $99.6675   $99.67   $99.65   $99.70  
  7 purchase totals = $985.57       $1,071.6705   $1,071.67   $1,071.65   $1,071.80