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 $58.67   5.544%   $61.9227   $61.92   $61.90   $61.90  
  Purchase #2 $75.76   4.685%   $79.3094   $79.31   $79.30   $79.30  
  Purchase #3 $118.83   10.834%   $131.704   $131.70   $131.70   $131.70  
  Purchase #4 $84.44   3.470%   $87.3701   $87.37   $87.35   $87.40  
  Purchase #5 $249.58   9.124%   $272.3517   $272.35   $272.35   $272.40  
  Purchase #6 $154.96   10.639%   $171.4462   $171.45   $171.45   $171.40  
  Purchase #7 $23.60   8.555%   $25.619   $25.62   $25.60   $25.60  
  7 purchase totals = $765.84       $829.7231   $829.72   $829.65   $829.70