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 $250.43   12.656%   $282.1244   $282.12   $282.10   $282.10  
  Purchase #2 $120.41   11.718%   $134.5196   $134.52   $134.50   $134.50  
  Purchase #3 $111.33   4.394%   $116.2218   $116.22   $116.20   $116.20  
  Purchase #4 $226.84   7.651%   $244.1955   $244.20   $244.20   $244.20  
  Purchase #5 $25.49   3.579%   $26.4023   $26.40   $26.40   $26.40  
  Purchase #6 $61.87   7.496%   $66.5078   $66.51   $66.50   $66.50  
  Purchase #7 $176.69   5.242%   $185.9521   $185.95   $185.95   $186.00  
  7 purchase totals = $973.06       $1,055.9235   $1,055.92   $1,055.85   $1,055.90