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 $205.45   4.169%   $214.0152   $214.02   $214.00   $214.00  
  Purchase #2 $64.81   7.405%   $69.6092   $69.61   $69.60   $69.60  
  Purchase #3 $29.45   11.636%   $32.8768   $32.88   $32.90   $32.90  
  Purchase #4 $80.85   6.104%   $85.7851   $85.79   $85.80   $85.80  
  Purchase #5 $147.72   4.254%   $154.004   $154.00   $154.00   $154.00  
  Purchase #6 $144.46   12.833%   $162.9986   $163.00   $163.00   $163.00  
  Purchase #7 $13.32   4.268%   $13.8885   $13.89   $13.90   $13.90  
  7 purchase totals = $686.06       $733.1774   $733.19   $733.20   $733.20