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 $147.34   11.863%   $164.8189   $164.82   $164.80   $164.80  
  Purchase #2 $248.67   12.368%   $279.4255   $279.43   $279.45   $279.40  
  Purchase #3 $195.48   6.807%   $208.7863   $208.79   $208.80   $208.80  
  Purchase #4 $112.87   6.569%   $120.2844   $120.28   $120.30   $120.30  
  Purchase #5 $64.30   6.690%   $68.6017   $68.60   $68.60   $68.60  
  Purchase #6 $206.41   6.693%   $220.225   $220.23   $220.25   $220.20  
  Purchase #7 $5.28   12.239%   $5.9262   $5.93   $5.95   $5.90  
  7 purchase totals = $980.35       $1,068.0680   $1,068.08   $1,068.15   $1,068.00