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 $48.62   3.126%   $50.1399   $50.14   $50.15   $50.10  
  Purchase #2 $209.67   11.581%   $233.9519   $233.95   $233.95   $234.00  
  Purchase #3 $113.57   8.613%   $123.3518   $123.35   $123.35   $123.40  
  Purchase #4 $104.89   5.189%   $110.3327   $110.33   $110.35   $110.30  
  Purchase #5 $179.99   3.598%   $186.466   $186.47   $186.45   $186.50  
  Purchase #6 $136.57   8.771%   $148.5486   $148.55   $148.55   $148.50  
  Purchase #7 $117.95   7.372%   $126.6453   $126.65   $126.65   $126.60  
  7 purchase totals = $911.26       $979.4362   $979.44   $979.45   $979.40