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 $82.77   13.527%   $93.9663   $93.97   $93.95   $94.00  
  Purchase #2 $15.36   6.294%   $16.3268   $16.33   $16.35   $16.30  
  Purchase #3 $26.41   8.447%   $28.6409   $28.64   $28.65   $28.60  
  Purchase #4 $175.45   5.329%   $184.7997   $184.80   $184.80   $184.80  
  Purchase #5 $35.57   10.446%   $39.2856   $39.29   $39.30   $39.30  
  Purchase #6 $178.66   13.264%   $202.3575   $202.36   $202.35   $202.40  
  Purchase #7 $165.54   3.629%   $171.5474   $171.55   $171.55   $171.50  
  7 purchase totals = $679.76       $736.9242   $736.94   $736.95   $736.90