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 $50.49   7.592%   $54.3232   $54.32   $54.30   $54.30  
  Purchase #2 $180.91   3.677%   $187.5621   $187.56   $187.55   $187.60  
  Purchase #3 $86.89   8.194%   $94.0098   $94.01   $94.00   $94.00  
  Purchase #4 $215.93   5.135%   $227.018   $227.02   $227.00   $227.00  
  Purchase #5 $96.50   8.241%   $104.4526   $104.45   $104.45   $104.50  
  Purchase #6 $80.48   13.726%   $91.5267   $91.53   $91.55   $91.50  
  Purchase #7 $59.99   13.688%   $68.2014   $68.20   $68.20   $68.20  
  7 purchase totals = $771.19       $827.0938   $827.09   $827.05   $827.10