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 $52.27   12.335%   $58.7175   $58.72   $58.70   $58.70  
  Purchase #2 $222.91   5.460%   $235.0809   $235.08   $235.10   $235.10  
  Purchase #3 $233.72   6.309%   $248.4654   $248.47   $248.45   $248.50  
  Purchase #4 $214.54   9.345%   $234.5888   $234.59   $234.60   $234.60  
  Purchase #5 $65.29   6.419%   $69.481   $69.48   $69.50   $69.50  
  Purchase #6 $194.79   10.112%   $214.4872   $214.49   $214.50   $214.50  
  Purchase #7 $167.36   6.590%   $178.389   $178.39   $178.40   $178.40  
  7 purchase totals = $1,150.88       $1,239.2098   $1,239.22   $1,239.25   $1,239.30