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 $171.48   12.416%   $192.771   $192.77   $192.75   $192.80  
  Purchase #2 $46.49   12.622%   $52.358   $52.36   $52.35   $52.40  
  Purchase #3 $246.62   7.198%   $264.3717   $264.37   $264.35   $264.40  
  Purchase #4 $186.66   3.769%   $193.6952   $193.70   $193.70   $193.70  
  Purchase #5 $151.80   11.393%   $169.0946   $169.09   $169.10   $169.10  
  Purchase #6 $133.58   4.479%   $139.563   $139.56   $139.55   $139.60  
  Purchase #7 $43.52   7.724%   $46.8815   $46.88   $46.90   $46.90  
  7 purchase totals = $980.15       $1,058.7350   $1,058.73   $1,058.70   $1,058.90