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 $205.72   13.620%   $233.7391   $233.74   $233.75   $233.70  
  Purchase #2 $23.60   11.387%   $26.2873   $26.29   $26.30   $26.30  
  Purchase #3 $114.66   4.118%   $119.3817   $119.38   $119.40   $119.40  
  Purchase #4 $62.39   7.818%   $67.2677   $67.27   $67.25   $67.30  
  Purchase #5 $213.81   4.473%   $223.3737   $223.37   $223.35   $223.40  
  Purchase #6 $9.76   12.340%   $10.9644   $10.96   $10.95   $11.00  
  Purchase #7 $78.80   10.117%   $86.7722   $86.77   $86.75   $86.80  
  7 purchase totals = $708.74       $767.7861   $767.78   $767.75   $767.90