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 $238.67   10.609%   $263.9905   $263.99   $264.00   $264.00  
  Purchase #2 $135.44   5.849%   $143.3619   $143.36   $143.35   $143.40  
  Purchase #3 $113.51   12.522%   $127.7237   $127.72   $127.70   $127.70  
  Purchase #4 $21.37   7.156%   $22.8992   $22.90   $22.90   $22.90  
  Purchase #5 $136.33   5.841%   $144.293   $144.29   $144.30   $144.30  
  Purchase #6 $107.52   13.120%   $121.6266   $121.63   $121.65   $121.60  
  Purchase #7 $215.54   8.790%   $234.486   $234.49   $234.50   $234.50  
  7 purchase totals = $968.38       $1,058.3809   $1,058.38   $1,058.40   $1,058.40