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 $149.38   8.232%   $161.677   $161.68   $161.70   $161.70  
  Purchase #2 $219.64   5.104%   $230.8504   $230.85   $230.85   $230.90  
  Purchase #3 $74.44   6.250%   $79.0925   $79.09   $79.10   $79.10  
  Purchase #4 $97.95   4.572%   $102.4283   $102.43   $102.45   $102.40  
  Purchase #5 $103.85   10.493%   $114.747   $114.75   $114.75   $114.70  
  Purchase #6 $150.32   9.673%   $164.8605   $164.86   $164.85   $164.90  
  Purchase #7 $139.96   5.691%   $147.9251   $147.93   $147.95   $147.90  
  7 purchase totals = $935.54       $1,001.5808   $1,001.59   $1,001.65   $1,001.60