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 $33.31   9.821%   $36.5814   $36.58   $36.60   $36.60  
  Purchase #2 $247.79   12.196%   $278.0105   $278.01   $278.00   $278.00  
  Purchase #3 $14.54   9.312%   $15.894   $15.89   $15.90   $15.90  
  Purchase #4 $133.81   13.438%   $151.7914   $151.79   $151.80   $151.80  
  Purchase #5 $170.68   8.361%   $184.9506   $184.95   $184.95   $185.00  
  Purchase #6 $220.92   10.239%   $243.54   $243.54   $243.55   $243.50  
  Purchase #7 $145.47   3.210%   $150.1396   $150.14   $150.15   $150.10  
  7 purchase totals = $966.52       $1,060.9075   $1,060.90   $1,060.95   $1,060.90