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 $93.27   13.840%   $106.1786   $106.18   $106.20   $106.20  
  Purchase #2 $78.33   10.359%   $86.4442   $86.44   $86.45   $86.40  
  Purchase #3 $56.52   3.336%   $58.4055   $58.41   $58.40   $58.40  
  Purchase #4 $172.46   13.398%   $195.5662   $195.57   $195.55   $195.60  
  Purchase #5 $183.29   8.168%   $198.2611   $198.26   $198.25   $198.30  
  Purchase #6 $225.32   9.757%   $247.3045   $247.30   $247.30   $247.30  
  Purchase #7 $115.68   12.194%   $129.786   $129.79   $129.80   $129.80  
  7 purchase totals = $924.87       $1,021.9461   $1,021.95   $1,021.95   $1,022.00