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 $58.89   8.508%   $63.9004   $63.90   $63.90   $63.90  
  Purchase #2 $228.42   5.675%   $241.3828   $241.38   $241.40   $241.40  
  Purchase #3 $204.68   5.850%   $216.6538   $216.65   $216.65   $216.70  
  Purchase #4 $52.82   6.563%   $56.2866   $56.29   $56.30   $56.30  
  Purchase #5 $32.36   8.640%   $35.1559   $35.16   $35.15   $35.20  
  Purchase #6 $76.64   10.574%   $84.7439   $84.74   $84.75   $84.70  
  Purchase #7 $34.65   11.516%   $38.6403   $38.64   $38.65   $38.60  
  7 purchase totals = $688.46       $736.7637   $736.76   $736.80   $736.80