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 $56.52   10.717%   $62.5772   $62.58   $62.60   $62.60  
  Purchase #2 $119.85   12.170%   $134.4357   $134.44   $134.45   $134.40  
  Purchase #3 $180.41   5.431%   $190.2081   $190.21   $190.20   $190.20  
  Purchase #4 $30.39   11.856%   $33.993   $33.99   $34.00   $34.00  
  Purchase #5 $70.49   8.434%   $76.4351   $76.44   $76.45   $76.40  
  Purchase #6 $115.53   6.846%   $123.4392   $123.44   $123.45   $123.40  
  Purchase #7 $218.44   7.803%   $235.4849   $235.48   $235.50   $235.50  
  7 purchase totals = $791.63       $856.5732   $856.58   $856.65   $856.50