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 $119.47   6.708%   $127.484   $127.48   $127.50   $127.50  
  Purchase #2 $81.56   3.706%   $84.5826   $84.58   $84.60   $84.60  
  Purchase #3 $120.57   4.858%   $126.4273   $126.43   $126.45   $126.40  
  Purchase #4 $241.39   9.630%   $264.6359   $264.64   $264.65   $264.60  
  Purchase #5 $104.85   9.623%   $114.9397   $114.94   $114.95   $114.90  
  Purchase #6 $24.53   6.336%   $26.0842   $26.08   $26.10   $26.10  
  Purchase #7 $28.40   9.248%   $31.0264   $31.03   $31.05   $31.00  
  7 purchase totals = $720.77       $775.1801   $775.18   $775.30   $775.10