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 $157.32   10.313%   $173.5444   $173.54   $173.55   $173.50  
  Purchase #2 $53.63   5.315%   $56.4804   $56.48   $56.50   $56.50  
  Purchase #3 $213.66   11.337%   $237.8826   $237.88   $237.90   $237.90  
  Purchase #4 $80.57   3.714%   $83.5624   $83.56   $83.55   $83.60  
  Purchase #5 $145.93   10.749%   $161.616   $161.62   $161.60   $161.60  
  Purchase #6 $176.49   13.768%   $200.7891   $200.79   $200.80   $200.80  
  Purchase #7 $153.93   9.585%   $168.6842   $168.68   $168.70   $168.70  
  7 purchase totals = $981.53       $1,082.5591   $1,082.55   $1,082.60   $1,082.60