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 $76.29   13.143%   $86.3168   $86.32   $86.30   $86.30  
  Purchase #2 $192.81   3.626%   $199.8013   $199.80   $199.80   $199.80  
  Purchase #3 $114.83   5.852%   $121.5499   $121.55   $121.55   $121.50  
  Purchase #4 $248.56   10.159%   $273.8112   $273.81   $273.80   $273.80  
  Purchase #5 $175.30   12.427%   $197.0845   $197.08   $197.10   $197.10  
  Purchase #6 $119.80   7.275%   $128.5155   $128.52   $128.50   $128.50  
  Purchase #7 $141.47   6.662%   $150.8947   $150.89   $150.90   $150.90  
  7 purchase totals = $1,069.06       $1,157.9739   $1,157.97   $1,157.95   $1,157.90