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 $238.54   9.143%   $260.3497   $260.35   $260.35   $260.30  
  Purchase #2 $169.67   8.551%   $184.1785   $184.18   $184.20   $184.20  
  Purchase #3 $160.27   7.296%   $171.9633   $171.96   $171.95   $172.00  
  Purchase #4 $190.79   6.529%   $203.2467   $203.25   $203.25   $203.20  
  Purchase #5 $11.81   6.815%   $12.6149   $12.61   $12.60   $12.60  
  Purchase #6 $74.44   12.212%   $83.5306   $83.53   $83.55   $83.50  
  Purchase #7 $147.37   8.110%   $159.3217   $159.32   $159.30   $159.30  
  7 purchase totals = $992.89       $1,075.2054   $1,075.20   $1,075.20   $1,075.10