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 $154.56   4.705%   $161.832   $161.83   $161.85   $161.80  
  Purchase #2 $241.45   13.252%   $273.447   $273.45   $273.45   $273.40  
  Purchase #3 $126.62   3.731%   $131.3442   $131.34   $131.35   $131.30  
  Purchase #4 $173.63   11.293%   $193.238   $193.24   $193.25   $193.20  
  Purchase #5 $33.54   6.732%   $35.7979   $35.80   $35.80   $35.80  
  Purchase #6 $210.93   7.109%   $225.925   $225.93   $225.95   $225.90  
  Purchase #7 $46.44   5.241%   $48.8739   $48.87   $48.85   $48.90  
  7 purchase totals = $987.17       $1,070.4580   $1,070.46   $1,070.50   $1,070.30