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 $141.56   8.297%   $153.3052   $153.31   $153.30   $153.30  
  Purchase #2 $150.42   10.351%   $165.99   $165.99   $166.00   $166.00  
  Purchase #3 $35.59   13.396%   $40.3576   $40.36   $40.35   $40.40  
  Purchase #4 $167.56   9.639%   $183.7111   $183.71   $183.70   $183.70  
  Purchase #5 $132.70   4.310%   $138.4194   $138.42   $138.40   $138.40  
  Purchase #6 $74.35   4.776%   $77.901   $77.90   $77.90   $77.90  
  Purchase #7 $242.49   4.710%   $253.9113   $253.91   $253.90   $253.90  
  7 purchase totals = $944.67       $1,013.5956   $1,013.60   $1,013.55   $1,013.60