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 $90.39   9.114%   $98.6281   $98.63   $98.65   $98.60  
  Purchase #2 $169.67   10.176%   $186.9356   $186.94   $186.95   $186.90  
  Purchase #3 $98.87   3.343%   $102.1752   $102.18   $102.20   $102.20  
  Purchase #4 $23.48   3.646%   $24.3361   $24.34   $24.35   $24.30  
  Purchase #5 $222.81   5.537%   $235.147   $235.15   $235.15   $235.10  
  Purchase #6 $181.92   5.682%   $192.2567   $192.26   $192.25   $192.30  
  Purchase #7 $191.87   7.799%   $206.8339   $206.83   $206.85   $206.80  
  7 purchase totals = $979.01       $1,046.3126   $1,046.33   $1,046.40   $1,046.20