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 $63.84   5.809%   $67.5485   $67.55   $67.55   $67.50  
  Purchase #2 $15.30   10.248%   $16.8679   $16.87   $16.85   $16.90  
  Purchase #3 $218.62   7.762%   $235.5893   $235.59   $235.60   $235.60  
  Purchase #4 $201.36   11.516%   $224.5486   $224.55   $224.55   $224.50  
  Purchase #5 $95.60   13.864%   $108.854   $108.85   $108.85   $108.90  
  Purchase #6 $118.46   10.399%   $130.7787   $130.78   $130.80   $130.80  
  Purchase #7 $136.53   3.328%   $141.0737   $141.07   $141.05   $141.10  
  7 purchase totals = $849.71       $925.2607   $925.26   $925.25   $925.30