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 $113.32   11.698%   $126.5762   $126.58   $126.60   $126.60  
  Purchase #2 $190.64   13.577%   $216.5232   $216.52   $216.50   $216.50  
  Purchase #3 $160.56   11.144%   $178.4528   $178.45   $178.45   $178.50  
  Purchase #4 $177.48   9.689%   $194.676   $194.68   $194.70   $194.70  
  Purchase #5 $53.27   13.121%   $60.2596   $60.26   $60.25   $60.30  
  Purchase #6 $208.80   4.716%   $218.647   $218.65   $218.65   $218.60  
  Purchase #7 $77.76   13.583%   $88.3221   $88.32   $88.30   $88.30  
  7 purchase totals = $981.83       $1,083.4569   $1,083.46   $1,083.45   $1,083.50