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 $31.96   4.209%   $33.3052   $33.31   $33.30   $33.30  
  Purchase #2 $228.66   3.470%   $236.5945   $236.59   $236.60   $236.60  
  Purchase #3 $101.73   11.135%   $113.0576   $113.06   $113.05   $113.10  
  Purchase #4 $75.73   3.713%   $78.5419   $78.54   $78.55   $78.50  
  Purchase #5 $232.57   13.448%   $263.846   $263.85   $263.85   $263.80  
  Purchase #6 $20.58   10.149%   $22.6687   $22.67   $22.65   $22.70  
  Purchase #7 $199.31   7.374%   $214.0071   $214.01   $214.00   $214.00  
  7 purchase totals = $890.54       $962.0210   $962.03   $962.00   $962.00