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 $38.70   9.205%   $42.2623   $42.26   $42.25   $42.30  
  Purchase #2 $182.98   11.688%   $204.3667   $204.37   $204.35   $204.40  
  Purchase #3 $120.84   4.813%   $126.656   $126.66   $126.65   $126.70  
  Purchase #4 $200.51   3.231%   $206.9885   $206.99   $207.00   $207.00  
  Purchase #5 $111.44   3.103%   $114.898   $114.90   $114.90   $114.90  
  Purchase #6 $185.53   9.168%   $202.5394   $202.54   $202.55   $202.50  
  Purchase #7 $112.57   13.402%   $127.6566   $127.66   $127.65   $127.70  
  7 purchase totals = $952.57       $1,025.3675   $1,025.38   $1,025.35   $1,025.50