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	$113.47	13.860%	$129.1969	$129.20	$129.20	$129.20
Purchase #2	$39.79	7.333%	$42.7078	$42.71	$42.70	$42.70
Purchase #3	$150.85	3.254%	$155.7587	$155.76	$155.75	$155.80
Purchase #4	$96.84	12.679%	$109.1183	$109.12	$109.10	$109.10
Purchase #5	$199.61	3.166%	$205.9297	$205.93	$205.95	$205.90
Purchase #6	$181.45	8.280%	$196.4741	$196.47	$196.45	$196.50
Purchase #7	$56.71	8.854%	$61.7311	$61.73	$61.75	$61.70
7 purchase totals =	$838.72		$900.9166	$900.92	$900.90	$900.90