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 $39.53   11.799%   $44.1941   $44.19   $44.20   $44.20  
  Purchase #2 $228.82   5.674%   $241.8032   $241.80   $241.80   $241.80  
  Purchase #3 $225.30   12.397%   $253.2304   $253.23   $253.25   $253.20  
  Purchase #4 $187.83   13.641%   $213.4519   $213.45   $213.45   $213.50  
  Purchase #5 $23.78   10.447%   $26.2643   $26.26   $26.25   $26.30  
  Purchase #6 $243.76   10.542%   $269.4572   $269.46   $269.45   $269.50  
  Purchase #7 $85.85   10.553%   $94.9098   $94.91   $94.90   $94.90  
  7 purchase totals = $1,034.87       $1,143.3109   $1,143.30   $1,143.30   $1,143.40