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 $196.43   11.126%   $218.2848   $218.28   $218.30   $218.30  
  Purchase #2 $201.35   3.310%   $208.0147   $208.01   $208.00   $208.00  
  Purchase #3 $36.87   4.473%   $38.5192   $38.52   $38.50   $38.50  
  Purchase #4 $151.48   6.585%   $161.455   $161.46   $161.45   $161.50  
  Purchase #5 $80.86   8.166%   $87.463   $87.46   $87.45   $87.50  
  Purchase #6 $191.72   12.462%   $215.6121   $215.61   $215.60   $215.60  
  Purchase #7 $165.58   12.314%   $185.9695   $185.97   $185.95   $186.00  
  7 purchase totals = $1,024.29       $1,115.3183   $1,115.31   $1,115.25   $1,115.40