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 $61.32   6.768%   $65.4701   $65.47   $65.45   $65.50  
  Purchase #2 $63.41   11.631%   $70.7852   $70.79   $70.80   $70.80  
  Purchase #3 $146.65   13.636%   $166.6472   $166.65   $166.65   $166.60  
  Purchase #4 $170.95   3.676%   $177.2341   $177.23   $177.25   $177.20  
  Purchase #5 $163.80   11.104%   $181.9884   $181.99   $182.00   $182.00  
  Purchase #6 $124.65   9.358%   $136.3147   $136.31   $136.30   $136.30  
  Purchase #7 $131.75   8.531%   $142.9896   $142.99   $143.00   $143.00  
  7 purchase totals = $862.53       $941.4293   $941.43   $941.45   $941.40