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 $138.95   9.816%   $152.5893   $152.59   $152.60   $152.60  
  Purchase #2 $244.48   10.109%   $269.1945   $269.19   $269.20   $269.20  
  Purchase #3 $108.32   6.665%   $115.5395   $115.54   $115.55   $115.50  
  Purchase #4 $235.93   6.208%   $250.5765   $250.58   $250.60   $250.60  
  Purchase #5 $175.69   10.210%   $193.6279   $193.63   $193.65   $193.60  
  Purchase #6 $60.94   4.425%   $63.6366   $63.64   $63.65   $63.60  
  Purchase #7 $131.65   6.802%   $140.6048   $140.60   $140.60   $140.60  
  7 purchase totals = $1,095.96       $1,185.7691   $1,185.77   $1,185.85   $1,185.70