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 $152.57   8.869%   $166.1014   $166.10   $166.10   $166.10  
  Purchase #2 $232.45   8.542%   $252.3059   $252.31   $252.30   $252.30  
  Purchase #3 $84.43   13.423%   $95.763   $95.76   $95.75   $95.80  
  Purchase #4 $77.58   9.777%   $85.165   $85.17   $85.15   $85.20  
  Purchase #5 $7.29   10.252%   $8.0374   $8.04   $8.05   $8.00  
  Purchase #6 $218.73   11.420%   $243.709   $243.71   $243.70   $243.70  
  Purchase #7 $70.56   7.715%   $76.0037   $76.00   $76.00   $76.00  
  7 purchase totals = $843.61       $927.0854   $927.09   $927.05   $927.10