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 $34.82   3.208%   $35.937   $35.94   $35.95   $35.90  
  Purchase #2 $26.86   3.494%   $27.7985   $27.80   $27.80   $27.80  
  Purchase #3 $85.93   3.146%   $88.6334   $88.63   $88.65   $88.60  
  Purchase #4 $186.63   4.831%   $195.6461   $195.65   $195.65   $195.60  
  Purchase #5 $118.61   13.239%   $134.3128   $134.31   $134.30   $134.30  
  Purchase #6 $65.84   6.413%   $70.0623   $70.06   $70.05   $70.10  
  Purchase #7 $32.79   11.422%   $36.5353   $36.54   $36.55   $36.50  
  7 purchase totals = $551.48       $588.9254   $588.93   $588.95   $588.80