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 $191.68   9.396%   $209.6903   $209.69   $209.70   $209.70  
  Purchase #2 $71.94   11.162%   $79.9699   $79.97   $79.95   $80.00  
  Purchase #3 $202.74   6.639%   $216.1999   $216.20   $216.20   $216.20  
  Purchase #4 $8.68   12.527%   $9.7673   $9.77   $9.75   $9.80  
  Purchase #5 $51.99   11.589%   $58.0151   $58.02   $58.00   $58.00  
  Purchase #6 $243.92   7.864%   $263.1019   $263.10   $263.10   $263.10  
  Purchase #7 $78.97   5.773%   $83.5289   $83.53   $83.55   $83.50  
  7 purchase totals = $849.92       $920.2733   $920.28   $920.25   $920.30