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	$114.81	13.689%	$130.5263	$130.53	$130.55	$130.50
Purchase #2	$201.95	11.340%	$224.8511	$224.85	$224.85	$224.90
Purchase #3	$54.91	12.416%	$61.7276	$61.73	$61.75	$61.70
Purchase #4	$80.57	12.206%	$90.4044	$90.40	$90.40	$90.40
Purchase #5	$55.37	3.370%	$57.236	$57.24	$57.25	$57.20
Purchase #6	$247.87	6.241%	$263.3396	$263.34	$263.35	$263.30
Purchase #7	$41.46	3.162%	$42.771	$42.77	$42.75	$42.80
7 purchase totals =	$796.94		$870.8560	$870.86	$870.90	$870.80