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 $51.33   8.371%   $55.6268   $55.63   $55.65   $55.60  
  Purchase #2 $175.78   4.798%   $184.2139   $184.21   $184.20   $184.20  
  Purchase #3 $54.90   11.593%   $61.2646   $61.26   $61.25   $61.30  
  Purchase #4 $176.98   6.416%   $188.335   $188.34   $188.35   $188.30  
  Purchase #5 $123.43   3.437%   $127.6723   $127.67   $127.65   $127.70  
  Purchase #6 $120.54   4.627%   $126.1174   $126.12   $126.10   $126.10  
  Purchase #7 $90.57   3.265%   $93.5271   $93.53   $93.55   $93.50  
  7 purchase totals = $793.53       $836.7571   $836.76   $836.75   $836.70