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 $62.41   8.255%   $67.5619   $67.56   $67.55   $67.60  
  Purchase #2 $157.72   13.488%   $178.9933   $178.99   $179.00   $179.00  
  Purchase #3 $226.48   12.115%   $253.9181   $253.92   $253.90   $253.90  
  Purchase #4 $154.93   8.357%   $167.8775   $167.88   $167.90   $167.90  
  Purchase #5 $18.37   9.578%   $20.1295   $20.13   $20.15   $20.10  
  Purchase #6 $36.63   7.335%   $39.3168   $39.32   $39.30   $39.30  
  Purchase #7 $199.54   11.656%   $222.7984   $222.80   $222.80   $222.80  
  7 purchase totals = $856.08       $950.5955   $950.60   $950.60   $950.60