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 $90.73   8.164%   $98.1372   $98.14   $98.15   $98.10  
  Purchase #2 $60.58   11.749%   $67.6975   $67.70   $67.70   $67.70  
  Purchase #3 $129.88   3.221%   $134.0634   $134.06   $134.05   $134.10  
  Purchase #4 $54.33   12.293%   $61.0088   $61.01   $61.00   $61.00  
  Purchase #5 $188.30   4.755%   $197.2537   $197.25   $197.25   $197.30  
  Purchase #6 $84.51   10.652%   $93.512   $93.51   $93.50   $93.50  
  Purchase #7 $128.56   11.684%   $143.581   $143.58   $143.60   $143.60  
  7 purchase totals = $736.89       $795.2536   $795.25   $795.25   $795.30