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	$80.53	12.196%	$90.3514	$90.35	$90.35	$90.40
Purchase #2	$215.48	11.292%	$239.812	$239.81	$239.80	$239.80
Purchase #3	$47.38	12.240%	$53.1793	$53.18	$53.20	$53.20
Purchase #4	$120.83	3.369%	$124.9008	$124.90	$124.90	$124.90
Purchase #5	$222.39	13.790%	$253.0576	$253.06	$253.05	$253.10
Purchase #6	$49.48	9.728%	$54.2934	$54.29	$54.30	$54.30
Purchase #7	$42.36	13.676%	$48.1532	$48.15	$48.15	$48.20
7 purchase totals =	$778.45		$863.7477	$863.74	$863.75	$863.90