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 $52.58   11.781%   $58.7744   $58.77   $58.75   $58.80  
  Purchase #2 $218.42   11.267%   $243.0294   $243.03   $243.05   $243.00  
  Purchase #3 $177.66   9.868%   $195.1915   $195.19   $195.20   $195.20  
  Purchase #4 $68.76   6.799%   $73.435   $73.44   $73.45   $73.40  
  Purchase #5 $16.83   11.194%   $18.714   $18.71   $18.70   $18.70  
  Purchase #6 $144.71   9.112%   $157.896   $157.90   $157.90   $157.90  
  Purchase #7 $224.26   13.332%   $254.1583   $254.16   $254.15   $254.20  
  7 purchase totals = $903.22       $1,001.1986   $1,001.20   $1,001.20   $1,001.20