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 $34.69   8.325%   $37.5779   $37.58   $37.60   $37.60  
  Purchase #2 $123.47   13.428%   $140.0496   $140.05   $140.05   $140.00  
  Purchase #3 $101.76   4.120%   $105.9525   $105.95   $105.95   $106.00  
  Purchase #4 $154.61   7.313%   $165.9166   $165.92   $165.90   $165.90  
  Purchase #5 $203.50   12.115%   $228.154   $228.15   $228.15   $228.20  
  Purchase #6 $8.42   7.596%   $9.0596   $9.06   $9.05   $9.10  
  Purchase #7 $239.62   8.573%   $260.1626   $260.16   $260.15   $260.20  
  7 purchase totals = $866.07       $946.8728   $946.87   $946.85   $947.00