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	$185.34	12.430%	$208.3778	$208.38	$208.40	$208.40
Purchase #2	$247.34	10.689%	$273.7782	$273.78	$273.80	$273.80
Purchase #3	$134.59	13.226%	$152.3909	$152.39	$152.40	$152.40
Purchase #4	$180.85	8.865%	$196.8824	$196.88	$196.90	$196.90
Purchase #5	$161.90	10.466%	$178.8445	$178.84	$178.85	$178.80
Purchase #6	$240.56	3.179%	$248.2074	$248.21	$248.20	$248.20
Purchase #7	$238.93	11.268%	$265.8526	$265.85	$265.85	$265.90
7 purchase totals =	$1,389.51		$1,524.3338	$1,524.33	$1,524.40	$1,524.40