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 $250.63   13.187%   $283.6806   $283.68   $283.70   $283.70  
  Purchase #2 $91.61   13.146%   $103.6531   $103.65   $103.65   $103.70  
  Purchase #3 $163.41   5.726%   $172.7669   $172.77   $172.75   $172.80  
  Purchase #4 $230.62   4.368%   $240.6935   $240.69   $240.70   $240.70  
  Purchase #5 $202.60   8.789%   $220.4065   $220.41   $220.40   $220.40  
  Purchase #6 $230.25   5.574%   $243.0841   $243.08   $243.10   $243.10  
  Purchase #7 $219.33   5.472%   $231.3317   $231.33   $231.35   $231.30  
  7 purchase totals = $1,388.45       $1,495.6164   $1,495.61   $1,495.65   $1,495.70