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 $96.59   8.268%   $104.5761   $104.58   $104.60   $104.60  
  Purchase #2 $114.90   8.348%   $124.4919   $124.49   $124.50   $124.50  
  Purchase #3 $51.45   6.467%   $54.7773   $54.78   $54.80   $54.80  
  Purchase #4 $163.60   4.828%   $171.4986   $171.50   $171.50   $171.50  
  Purchase #5 $192.77   11.445%   $214.8325   $214.83   $214.85   $214.80  
  Purchase #6 $35.50   10.732%   $39.3099   $39.31   $39.30   $39.30  
  Purchase #7 $144.59   7.348%   $155.2145   $155.21   $155.20   $155.20  
  7 purchase totals = $799.40       $864.7008   $864.70   $864.75   $864.70