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 $224.26   7.868%   $241.9048   $241.90   $241.90   $241.90  
  Purchase #2 $229.50   13.238%   $259.8812   $259.88   $259.90   $259.90  
  Purchase #3 $63.25   12.730%   $71.3017   $71.30   $71.30   $71.30  
  Purchase #4 $109.94   9.612%   $120.5074   $120.51   $120.50   $120.50  
  Purchase #5 $106.48   11.560%   $118.7891   $118.79   $118.80   $118.80  
  Purchase #6 $222.81   9.172%   $243.2461   $243.25   $243.25   $243.20  
  Purchase #7 $27.93   7.589%   $30.0496   $30.05   $30.05   $30.00  
  7 purchase totals = $984.17       $1,085.6799   $1,085.68   $1,085.70   $1,085.60