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 $62.94   6.497%   $67.0292   $67.03   $67.05   $67.00  
  Purchase #2 $224.54   6.136%   $238.3178   $238.32   $238.30   $238.30  
  Purchase #3 $74.56   7.193%   $79.9231   $79.92   $79.90   $79.90  
  Purchase #4 $142.35   3.613%   $147.4931   $147.49   $147.50   $147.50  
  Purchase #5 $154.85   8.124%   $167.43   $167.43   $167.45   $167.40  
  Purchase #6 $76.74   12.646%   $86.4445   $86.44   $86.45   $86.40  
  Purchase #7 $44.51   11.112%   $49.456   $49.46   $49.45   $49.50  
  7 purchase totals = $780.49       $836.0937   $836.09   $836.10   $836.00