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 $91.81   11.778%   $102.6234   $102.62   $102.60   $102.60  
  Purchase #2 $220.74   9.245%   $241.1474   $241.15   $241.15   $241.10  
  Purchase #3 $149.69   4.627%   $156.6162   $156.62   $156.60   $156.60  
  Purchase #4 $248.35   9.402%   $271.6999   $271.70   $271.70   $271.70  
  Purchase #5 $7.96   7.292%   $8.5404   $8.54   $8.55   $8.50  
  Purchase #6 $177.32   9.254%   $193.7292   $193.73   $193.75   $193.70  
  Purchase #7 $60.29   5.660%   $63.7024   $63.70   $63.70   $63.70  
  7 purchase totals = $956.16       $1,038.0589   $1,038.06   $1,038.05   $1,037.90