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 $119.26   12.796%   $134.5205   $134.52   $134.50   $134.50  
  Purchase #2 $40.33   11.326%   $44.8978   $44.90   $44.90   $44.90  
  Purchase #3 $111.95   10.743%   $123.9768   $123.98   $124.00   $124.00  
  Purchase #4 $68.90   6.873%   $73.6355   $73.64   $73.65   $73.60  
  Purchase #5 $10.69   5.198%   $11.2457   $11.25   $11.25   $11.20  
  Purchase #6 $160.61   4.313%   $167.5371   $167.54   $167.55   $167.50  
  Purchase #7 $234.30   5.240%   $246.5773   $246.58   $246.60   $246.60  
  7 purchase totals = $746.04       $802.3907   $802.41   $802.45   $802.30