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 $125.67   11.623%   $140.2766   $140.28   $140.30   $140.30  
  Purchase #2 $249.88   11.399%   $278.3638   $278.36   $278.35   $278.40  
  Purchase #3 $78.49   13.815%   $89.3334   $89.33   $89.35   $89.30  
  Purchase #4 $181.30   6.696%   $193.4398   $193.44   $193.45   $193.40  
  Purchase #5 $148.46   8.487%   $161.0598   $161.06   $161.05   $161.10  
  Purchase #6 $73.25   9.773%   $80.4087   $80.41   $80.40   $80.40  
  Purchase #7 $106.56   13.436%   $120.8774   $120.88   $120.90   $120.90  
  7 purchase totals = $963.61       $1,063.7595   $1,063.76   $1,063.80   $1,063.80