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 $226.99   4.855%   $238.0104   $238.01   $238.00   $238.00  
  Purchase #2 $152.38   8.677%   $165.602   $165.60   $165.60   $165.60  
  Purchase #3 $71.46   8.553%   $77.572   $77.57   $77.55   $77.60  
  Purchase #4 $158.26   5.431%   $166.8551   $166.86   $166.85   $166.90  
  Purchase #5 $73.43   3.727%   $76.1667   $76.17   $76.15   $76.20  
  Purchase #6 $168.58   7.824%   $181.7697   $181.77   $181.75   $181.80  
  Purchase #7 $243.93   10.119%   $268.6133   $268.61   $268.60   $268.60  
  7 purchase totals = $1,095.03       $1,174.5892   $1,174.59   $1,174.50   $1,174.70