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 $192.55   6.495%   $205.0561   $205.06   $205.05   $205.10  
  Purchase #2 $41.75   13.235%   $47.2756   $47.28   $47.30   $47.30  
  Purchase #3 $183.70   7.194%   $196.9154   $196.92   $196.90   $196.90  
  Purchase #4 $125.39   11.517%   $139.8312   $139.83   $139.85   $139.80  
  Purchase #5 $65.96   3.255%   $68.107   $68.11   $68.10   $68.10  
  Purchase #6 $153.50   3.425%   $158.7574   $158.76   $158.75   $158.80  
  Purchase #7 $217.50   11.476%   $242.4603   $242.46   $242.45   $242.50  
  7 purchase totals = $980.35       $1,058.4030   $1,058.42   $1,058.40   $1,058.50