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	$51.57	12.821%	$58.1818	$58.18	$58.20	$58.20
Purchase #2	$88.63	9.705%	$97.2315	$97.23	$97.25	$97.20
Purchase #3	$28.75	13.244%	$32.5577	$32.56	$32.55	$32.60
Purchase #4	$129.91	13.238%	$147.1075	$147.11	$147.10	$147.10
Purchase #5	$185.67	5.855%	$196.541	$196.54	$196.55	$196.50
Purchase #6	$85.94	3.467%	$88.9195	$88.92	$88.90	$88.90
Purchase #7	$198.76	3.558%	$205.8319	$205.83	$205.85	$205.80
7 purchase totals =	$769.23		$826.3709	$826.37	$826.40	$826.30