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	$50.69	5.131%	$53.2909	$53.29	$53.30	$53.30
Purchase #2	$43.75	7.234%	$46.9149	$46.91	$46.90	$46.90
Purchase #3	$39.31	5.362%	$41.4178	$41.42	$41.40	$41.40
Purchase #4	$239.85	10.801%	$265.7562	$265.76	$265.75	$265.80
Purchase #5	$134.96	9.790%	$148.1726	$148.17	$148.15	$148.20
Purchase #6	$86.89	13.353%	$98.4924	$98.49	$98.50	$98.50
Purchase #7	$186.25	12.453%	$209.4437	$209.44	$209.45	$209.40
7 purchase totals =	$781.70		$863.4885	$863.48	$863.45	$863.50