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 $111.54   13.197%   $126.2599   $126.26   $126.25   $126.30  
  Purchase #2 $51.58   5.131%   $54.2266   $54.23   $54.25   $54.20  
  Purchase #3 $208.35   5.253%   $219.2946   $219.29   $219.30   $219.30  
  Purchase #4 $56.78   9.220%   $62.0151   $62.02   $62.00   $62.00  
  Purchase #5 $209.52   8.102%   $226.4953   $226.50   $226.50   $226.50  
  Purchase #6 $185.32   3.538%   $191.8766   $191.88   $191.90   $191.90  
  Purchase #7 $186.84   3.601%   $193.5681   $193.57   $193.55   $193.60  
  7 purchase totals = $1,009.93       $1,073.7362   $1,073.75   $1,073.75   $1,073.80