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	$156.45	11.447%	$174.3588	$174.36	$174.35	$174.40
Purchase #2	$82.95	8.501%	$90.0016	$90.00	$90.00	$90.00
Purchase #3	$175.90	9.277%	$192.2182	$192.22	$192.20	$192.20
Purchase #4	$196.88	13.112%	$222.6949	$222.69	$222.70	$222.70
Purchase #5	$73.57	3.179%	$75.9088	$75.91	$75.90	$75.90
Purchase #6	$22.98	11.581%	$25.6413	$25.64	$25.65	$25.60
Purchase #7	$217.76	10.251%	$240.0826	$240.08	$240.10	$240.10
7 purchase totals =	$926.49		$1,020.9062	$1,020.90	$1,020.90	$1,020.90