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 $236.35   6.822%   $252.4738   $252.47   $252.45   $252.50  
  Purchase #2 $56.84   5.847%   $60.1634   $60.16   $60.15   $60.20  
  Purchase #3 $150.88   3.767%   $156.5636   $156.56   $156.55   $156.60  
  Purchase #4 $233.59   11.163%   $259.6657   $259.67   $259.65   $259.70  
  Purchase #5 $29.37   4.399%   $30.662   $30.66   $30.65   $30.70  
  Purchase #6 $175.94   3.527%   $182.1454   $182.15   $182.15   $182.10  
  Purchase #7 $211.97   11.599%   $236.5564   $236.56   $236.55   $236.60  
  7 purchase totals = $1,094.94       $1,178.2303   $1,178.23   $1,178.15   $1,178.40