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 $58.44   5.781%   $61.8184   $61.82   $61.80   $61.80  
  Purchase #2 $5.87   4.704%   $6.1461   $6.15   $6.15   $6.10  
  Purchase #3 $53.70   9.238%   $58.6608   $58.66   $58.65   $58.70  
  Purchase #4 $48.99   7.825%   $52.8235   $52.82   $52.80   $52.80  
  Purchase #5 $199.66   4.139%   $207.9239   $207.92   $207.90   $207.90  
  Purchase #6 $243.37   8.428%   $263.8812   $263.88   $263.90   $263.90  
  Purchase #7 $165.62   4.233%   $172.6307   $172.63   $172.65   $172.60  
  7 purchase totals = $775.65       $823.8846   $823.88   $823.85   $823.80