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 $77.58   11.150%   $86.2302   $86.23   $86.25   $86.20  
  Purchase #2 $59.32   6.696%   $63.2921   $63.29   $63.30   $63.30  
  Purchase #3 $166.71   3.485%   $172.5198   $172.52   $172.50   $172.50  
  Purchase #4 $204.65   5.541%   $215.9897   $215.99   $216.00   $216.00  
  Purchase #5 $26.40   12.452%   $29.6873   $29.69   $29.70   $29.70  
  Purchase #6 $184.25   9.699%   $202.1204   $202.12   $202.10   $202.10  
  Purchase #7 $175.50   10.420%   $193.7871   $193.79   $193.80   $193.80  
  7 purchase totals = $894.41       $963.6266   $963.63   $963.65   $963.60