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 $54.35   4.155%   $56.6082   $56.61   $56.60   $56.60  
  Purchase #2 $177.71   9.275%   $194.1926   $194.19   $194.20   $194.20  
  Purchase #3 $80.72   8.325%   $87.4399   $87.44   $87.45   $87.40  
  Purchase #4 $15.39   9.378%   $16.8333   $16.83   $16.85   $16.80  
  Purchase #5 $214.55   5.529%   $226.4125   $226.41   $226.40   $226.40  
  Purchase #6 $28.98   11.355%   $32.2707   $32.27   $32.25   $32.30  
  Purchase #7 $173.85   3.273%   $179.5401   $179.54   $179.55   $179.50  
  7 purchase totals = $745.55       $793.2973   $793.29   $793.30   $793.20