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 $248.32   8.704%   $269.9338   $269.93   $269.95   $269.90  
  Purchase #2 $90.40   13.770%   $102.8481   $102.85   $102.85   $102.80  
  Purchase #3 $32.50   3.209%   $33.5429   $33.54   $33.55   $33.50  
  Purchase #4 $113.47   6.425%   $120.7604   $120.76   $120.75   $120.80  
  Purchase #5 $116.74   6.449%   $124.2686   $124.27   $124.25   $124.30  
  Purchase #6 $31.64   11.313%   $35.2194   $35.22   $35.20   $35.20  
  Purchase #7 $124.36   4.317%   $129.7286   $129.73   $129.75   $129.70  
  7 purchase totals = $757.43       $816.3018   $816.30   $816.30   $816.20