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 $190.57   7.258%   $204.4016   $204.40   $204.40   $204.40  
  Purchase #2 $233.95   4.852%   $245.3013   $245.30   $245.30   $245.30  
  Purchase #3 $53.82   8.120%   $58.1902   $58.19   $58.20   $58.20  
  Purchase #4 $106.29   7.595%   $114.3627   $114.36   $114.35   $114.40  
  Purchase #5 $243.86   5.841%   $258.1039   $258.10   $258.10   $258.10  
  Purchase #6 $250.47   11.761%   $279.9278   $279.93   $279.95   $279.90  
  Purchase #7 $34.27   3.159%   $35.3526   $35.35   $35.35   $35.40  
  7 purchase totals = $1,113.23       $1,195.6401   $1,195.63   $1,195.65   $1,195.70