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 $134.88   13.287%   $152.8015   $152.80   $152.80   $152.80  
  Purchase #2 $72.86   12.756%   $82.154   $82.15   $82.15   $82.20  
  Purchase #3 $171.73   8.286%   $185.9595   $185.96   $185.95   $186.00  
  Purchase #4 $122.34   9.422%   $133.8669   $133.87   $133.85   $133.90  
  Purchase #5 $84.98   6.308%   $90.3405   $90.34   $90.35   $90.30  
  Purchase #6 $141.32   7.703%   $152.2059   $152.21   $152.20   $152.20  
  Purchase #7 $214.97   5.503%   $226.7998   $226.80   $226.80   $226.80  
  7 purchase totals = $943.08       $1,024.1281   $1,024.13   $1,024.10   $1,024.20