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 $209.93   12.837%   $236.8787   $236.88   $236.90   $236.90  
  Purchase #2 $67.39   3.208%   $69.5519   $69.55   $69.55   $69.60  
  Purchase #3 $149.35   13.154%   $168.9955   $169.00   $169.00   $169.00  
  Purchase #4 $188.56   4.486%   $197.0188   $197.02   $197.00   $197.00  
  Purchase #5 $117.45   12.121%   $131.6861   $131.69   $131.70   $131.70  
  Purchase #6 $213.76   6.655%   $227.9857   $227.99   $228.00   $228.00  
  Purchase #7 $63.61   3.745%   $65.9922   $65.99   $66.00   $66.00  
  7 purchase totals = $1,010.05       $1,098.1089   $1,098.12   $1,098.15   $1,098.20