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 $25.34   4.827%   $26.5632   $26.56   $26.55   $26.60  
  Purchase #2 $181.28   3.169%   $187.0248   $187.02   $187.00   $187.00  
  Purchase #3 $182.45   8.331%   $197.6499   $197.65   $197.65   $197.60  
  Purchase #4 $124.48   13.432%   $141.2002   $141.20   $141.20   $141.20  
  Purchase #5 $50.26   6.417%   $53.4852   $53.49   $53.50   $53.50  
  Purchase #6 $219.26   12.116%   $245.8255   $245.83   $245.85   $245.80  
  Purchase #7 $14.43   9.295%   $15.7713   $15.77   $15.75   $15.80  
  7 purchase totals = $797.50       $867.5201   $867.52   $867.50   $867.50