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 $61.26   12.383%   $68.8458   $68.85   $68.85   $68.80  
  Purchase #2 $193.99   9.842%   $213.0825   $213.08   $213.10   $213.10  
  Purchase #3 $55.91   12.141%   $62.698   $62.70   $62.70   $62.70  
  Purchase #4 $57.84   10.247%   $63.7669   $63.77   $63.75   $63.80  
  Purchase #5 $103.40   5.497%   $109.0839   $109.08   $109.10   $109.10  
  Purchase #6 $177.85   8.351%   $192.7023   $192.70   $192.70   $192.70  
  Purchase #7 $131.52   11.833%   $147.0828   $147.08   $147.10   $147.10  
  7 purchase totals = $781.77       $857.2622   $857.26   $857.30   $857.30