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 $59.95   3.162%   $61.8456   $61.85   $61.85   $61.80  
  Purchase #2 $23.28   4.746%   $24.3849   $24.38   $24.40   $24.40  
  Purchase #3 $156.32   4.150%   $162.8073   $162.81   $162.80   $162.80  
  Purchase #4 $220.98   13.729%   $251.3183   $251.32   $251.30   $251.30  
  Purchase #5 $130.79   4.198%   $136.2806   $136.28   $136.30   $136.30  
  Purchase #6 $19.47   11.712%   $21.7503   $21.75   $21.75   $21.80  
  Purchase #7 $203.77   3.744%   $211.3991   $211.40   $211.40   $211.40  
  7 purchase totals = $814.56       $869.7861   $869.79   $869.80   $869.80