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 $63.88   4.150%   $66.531   $66.53   $66.55   $66.50  
  Purchase #2 $189.77   12.835%   $214.127   $214.13   $214.15   $214.10  
  Purchase #3 $58.50   10.591%   $64.6957   $64.70   $64.70   $64.70  
  Purchase #4 $65.52   7.527%   $70.4517   $70.45   $70.45   $70.50  
  Purchase #5 $175.27   4.572%   $183.2833   $183.28   $183.30   $183.30  
  Purchase #6 $85.97   8.133%   $92.9619   $92.96   $92.95   $93.00  
  Purchase #7 $200.88   5.589%   $212.1072   $212.11   $212.10   $212.10  
  7 purchase totals = $839.79       $904.1578   $904.16   $904.20   $904.20