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 $196.26   11.370%   $218.5748   $218.57   $218.55   $218.60  
  Purchase #2 $134.63   12.137%   $150.97   $150.97   $150.95   $151.00  
  Purchase #3 $52.38   12.402%   $58.8762   $58.88   $58.90   $58.90  
  Purchase #4 $94.48   7.318%   $101.394   $101.39   $101.40   $101.40  
  Purchase #5 $218.97   8.625%   $237.8562   $237.86   $237.85   $237.90  
  Purchase #6 $239.44   9.771%   $262.8357   $262.84   $262.85   $262.80  
  Purchase #7 $26.43   5.615%   $27.914   $27.91   $27.90   $27.90  
  7 purchase totals = $962.59       $1,058.4209   $1,058.42   $1,058.40   $1,058.50