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 $178.96   12.792%   $201.8526   $201.85   $201.85   $201.90  
  Purchase #2 $134.59   4.550%   $140.7138   $140.71   $140.70   $140.70  
  Purchase #3 $11.42   7.732%   $12.303   $12.30   $12.30   $12.30  
  Purchase #4 $174.61   9.171%   $190.6235   $190.62   $190.60   $190.60  
  Purchase #5 $114.26   4.795%   $119.7388   $119.74   $119.75   $119.70  
  Purchase #6 $161.86   6.247%   $171.9714   $171.97   $171.95   $172.00  
  Purchase #7 $206.47   6.407%   $219.6985   $219.70   $219.70   $219.70  
  7 purchase totals = $982.17       $1,056.9016   $1,056.89   $1,056.85   $1,056.90