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 $236.41   13.779%   $268.9849   $268.98   $269.00   $269.00  
  Purchase #2 $58.30   8.724%   $63.3861   $63.39   $63.40   $63.40  
  Purchase #3 $100.27   12.357%   $112.6604   $112.66   $112.65   $112.70  
  Purchase #4 $147.49   9.650%   $161.7228   $161.72   $161.70   $161.70  
  Purchase #5 $96.95   7.533%   $104.2532   $104.25   $104.25   $104.30  
  Purchase #6 $216.41   13.746%   $246.1577   $246.16   $246.15   $246.20  
  Purchase #7 $150.48   8.237%   $162.875   $162.88   $162.90   $162.90  
  7 purchase totals = $1,006.31       $1,120.0401   $1,120.04   $1,120.05   $1,120.20