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 $207.93   12.109%   $233.1082   $233.11   $233.10   $233.10  
  Purchase #2 $63.97   10.430%   $70.6421   $70.64   $70.65   $70.60  
  Purchase #3 $169.99   3.203%   $175.4348   $175.43   $175.45   $175.40  
  Purchase #4 $240.91   5.775%   $254.8226   $254.82   $254.80   $254.80  
  Purchase #5 $155.83   3.208%   $160.829   $160.83   $160.85   $160.80  
  Purchase #6 $121.41   4.209%   $126.5201   $126.52   $126.50   $126.50  
  Purchase #7 $177.53   9.447%   $194.3013   $194.30   $194.30   $194.30  
  7 purchase totals = $1,137.57       $1,215.6581   $1,215.65   $1,215.65   $1,215.50