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 $183.29   5.759%   $193.8457   $193.85   $193.85   $193.80  
  Purchase #2 $22.82   13.326%   $25.861   $25.86   $25.85   $25.90  
  Purchase #3 $134.71   6.848%   $143.9349   $143.93   $143.95   $143.90  
  Purchase #4 $46.94   5.448%   $49.4973   $49.50   $49.50   $49.50  
  Purchase #5 $226.58   9.282%   $247.6112   $247.61   $247.60   $247.60  
  Purchase #6 $176.91   7.605%   $190.364   $190.36   $190.35   $190.40  
  Purchase #7 $168.95   13.770%   $192.2144   $192.21   $192.20   $192.20  
  7 purchase totals = $960.20       $1,043.3285   $1,043.32   $1,043.30   $1,043.30