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 $93.50   9.691%   $102.5611   $102.56   $102.55   $102.60  
  Purchase #2 $208.50   12.127%   $233.7848   $233.78   $233.80   $233.80  
  Purchase #3 $12.88   13.847%   $14.6635   $14.66   $14.65   $14.70  
  Purchase #4 $132.28   13.201%   $149.7423   $149.74   $149.75   $149.70  
  Purchase #5 $239.64   13.328%   $271.5792   $271.58   $271.60   $271.60  
  Purchase #6 $83.33   3.289%   $86.0707   $86.07   $86.05   $86.10  
  Purchase #7 $134.66   6.160%   $142.9551   $142.96   $142.95   $143.00  
  7 purchase totals = $904.79       $1,001.3567   $1,001.35   $1,001.35   $1,001.50