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 $196.77   10.657%   $217.7398   $217.74   $217.75   $217.70  
  Purchase #2 $23.51   4.590%   $24.5891   $24.59   $24.60   $24.60  
  Purchase #3 $184.63   3.173%   $190.4883   $190.49   $190.50   $190.50  
  Purchase #4 $82.27   6.437%   $87.5657   $87.57   $87.55   $87.60  
  Purchase #5 $225.53   3.561%   $233.5611   $233.56   $233.55   $233.60  
  Purchase #6 $195.48   12.523%   $219.96   $219.96   $219.95   $220.00  
  Purchase #7 $6.97   4.332%   $7.2719   $7.27   $7.25   $7.30  
  7 purchase totals = $915.16       $981.1759   $981.18   $981.15   $981.30