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 $243.86   6.858%   $260.5839   $260.58   $260.60   $260.60  
  Purchase #2 $61.30   10.332%   $67.6335   $67.63   $67.65   $67.60  
  Purchase #3 $86.84   5.196%   $91.3522   $91.35   $91.35   $91.40  
  Purchase #4 $164.62   4.516%   $172.0542   $172.05   $172.05   $172.10  
  Purchase #5 $26.89   13.321%   $30.472   $30.47   $30.45   $30.50  
  Purchase #6 $178.55   13.369%   $202.4203   $202.42   $202.40   $202.40  
  Purchase #7 $70.77   12.456%   $79.5851   $79.59   $79.60   $79.60  
  7 purchase totals = $832.83       $904.1012   $904.09   $904.10   $904.20