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 $144.65   11.272%   $160.9549   $160.95   $160.95   $161.00  
  Purchase #2 $226.28   4.571%   $236.6233   $236.62   $236.60   $236.60  
  Purchase #3 $187.30   8.863%   $203.9004   $203.90   $203.90   $203.90  
  Purchase #4 $54.97   3.787%   $57.0517   $57.05   $57.05   $57.10  
  Purchase #5 $13.93   4.445%   $14.5492   $14.55   $14.55   $14.50  
  Purchase #6 $77.88   3.250%   $80.4111   $80.41   $80.40   $80.40  
  Purchase #7 $90.41   4.110%   $94.1259   $94.13   $94.15   $94.10  
  7 purchase totals = $795.42       $847.6165   $847.61   $847.60   $847.60