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 $31.81   6.760%   $33.9604   $33.96   $33.95   $34.00  
  Purchase #2 $187.83   8.379%   $203.5683   $203.57   $203.55   $203.60  
  Purchase #3 $6.69   5.388%   $7.0505   $7.05   $7.05   $7.10  
  Purchase #4 $248.26   7.561%   $267.0309   $267.03   $267.05   $267.00  
  Purchase #5 $37.80   4.631%   $39.5505   $39.55   $39.55   $39.60  
  Purchase #6 $249.36   6.275%   $265.0073   $265.01   $265.00   $265.00  
  Purchase #7 $219.39   3.710%   $227.5294   $227.53   $227.55   $227.50  
  7 purchase totals = $981.14       $1,043.6973   $1,043.70   $1,043.70   $1,043.80