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 $60.84   4.514%   $63.5863   $63.59   $63.60   $63.60  
  Purchase #2 $165.75   10.432%   $183.041   $183.04   $183.05   $183.00  
  Purchase #3 $79.82   10.467%   $88.1748   $88.17   $88.15   $88.20  
  Purchase #4 $235.81   13.453%   $267.5335   $267.53   $267.55   $267.50  
  Purchase #5 $5.92   5.452%   $6.2428   $6.24   $6.25   $6.20  
  Purchase #6 $236.25   8.220%   $255.6698   $255.67   $255.65   $255.70  
  Purchase #7 $76.83   5.634%   $81.1586   $81.16   $81.15   $81.20  
  7 purchase totals = $861.22       $945.4068   $945.40   $945.40   $945.40