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 $54.69   12.455%   $61.5016   $61.50   $61.50   $61.50  
  Purchase #2 $143.88   3.102%   $148.3432   $148.34   $148.35   $148.30  
  Purchase #3 $179.81   4.751%   $188.3528   $188.35   $188.35   $188.40  
  Purchase #4 $90.34   13.687%   $102.7048   $102.70   $102.70   $102.70  
  Purchase #5 $92.40   4.494%   $96.5525   $96.55   $96.55   $96.60  
  Purchase #6 $231.25   9.116%   $252.3308   $252.33   $252.35   $252.30  
  Purchase #7 $141.99   6.846%   $151.7106   $151.71   $151.70   $151.70  
  7 purchase totals = $934.36       $1,001.4963   $1,001.48   $1,001.50   $1,001.50