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 $41.98   12.722%   $47.3207   $47.32   $47.30   $47.30  
  Purchase #2 $26.46   9.261%   $28.9105   $28.91   $28.90   $28.90  
  Purchase #3 $152.59   13.593%   $173.3316   $173.33   $173.35   $173.30  
  Purchase #4 $76.41   11.593%   $85.2682   $85.27   $85.25   $85.30  
  Purchase #5 $130.40   10.470%   $144.0529   $144.05   $144.05   $144.10  
  Purchase #6 $150.44   4.351%   $156.9856   $156.99   $157.00   $157.00  
  Purchase #7 $214.28   5.288%   $225.6111   $225.61   $225.60   $225.60  
  7 purchase totals = $792.56       $861.4806   $861.48   $861.45   $861.50