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 $36.83   4.372%   $38.4402   $38.44   $38.45   $38.40  
  Purchase #2 $189.73   9.761%   $208.2495   $208.25   $208.25   $208.20  
  Purchase #3 $202.58   4.246%   $211.1815   $211.18   $211.20   $211.20  
  Purchase #4 $49.89   12.285%   $56.019   $56.02   $56.00   $56.00  
  Purchase #5 $156.27   3.149%   $161.1909   $161.19   $161.20   $161.20  
  Purchase #6 $44.35   5.113%   $46.6176   $46.62   $46.60   $46.60  
  Purchase #7 $61.46   13.220%   $69.585   $69.59   $69.60   $69.60  
  7 purchase totals = $741.11       $791.2837   $791.29   $791.30   $791.20