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 $107.80   10.280%   $118.8818   $118.88   $118.90   $118.90  
  Purchase #2 $227.35   11.725%   $254.0068   $254.01   $254.00   $254.00  
  Purchase #3 $49.74   7.745%   $53.5924   $53.59   $53.60   $53.60  
  Purchase #4 $70.63   5.737%   $74.682   $74.68   $74.70   $74.70  
  Purchase #5 $233.83   5.770%   $247.322   $247.32   $247.30   $247.30  
  Purchase #6 $96.37   5.500%   $101.6704   $101.67   $101.65   $101.70  
  Purchase #7 $118.90   6.484%   $126.6095   $126.61   $126.60   $126.60  
  7 purchase totals = $904.62       $976.7649   $976.76   $976.75   $976.80