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	$83.73	5.264%	$88.1375	$88.14	$88.15	$88.10
Purchase #2	$50.31	9.171%	$54.9239	$54.92	$54.90	$54.90
Purchase #3	$6.34	7.854%	$6.8379	$6.84	$6.85	$6.80
Purchase #4	$239.29	13.107%	$270.6537	$270.65	$270.65	$270.70
Purchase #5	$38.75	8.801%	$42.1604	$42.16	$42.15	$42.20
Purchase #6	$32.79	3.517%	$33.9432	$33.94	$33.95	$33.90
Purchase #7	$19.55	3.655%	$20.2646	$20.26	$20.25	$20.30
7 purchase totals =	$470.76		$516.9212	$516.91	$516.90	$516.90