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 $112.31   13.555%   $127.5336   $127.53   $127.55   $127.50  
  Purchase #2 $143.28   8.215%   $155.0505   $155.05   $155.05   $155.10  
  Purchase #3 $116.67   6.588%   $124.3562   $124.36   $124.35   $124.40  
  Purchase #4 $214.43   9.346%   $234.4706   $234.47   $234.45   $234.50  
  Purchase #5 $71.41   7.566%   $76.8129   $76.81   $76.80   $76.80  
  Purchase #6 $228.59   10.415%   $252.3976   $252.40   $252.40   $252.40  
  Purchase #7 $221.95   6.301%   $235.9351   $235.94   $235.95   $235.90  
  7 purchase totals = $1,108.64       $1,206.5565   $1,206.56   $1,206.55   $1,206.60