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	$188.31	4.217%	$196.251	$196.25	$196.25	$196.30
Purchase #2	$97.91	7.782%	$105.5294	$105.53	$105.55	$105.50
Purchase #3	$155.75	6.502%	$165.8769	$165.88	$165.90	$165.90
Purchase #4	$55.66	7.696%	$59.9436	$59.94	$59.95	$59.90
Purchase #5	$125.67	11.196%	$139.74	$139.74	$139.75	$139.70
Purchase #6	$232.57	5.636%	$245.6776	$245.68	$245.70	$245.70
Purchase #7	$92.59	13.520%	$105.1082	$105.11	$105.10	$105.10
7 purchase totals =	$948.46		$1,018.1267	$1,018.13	$1,018.20	$1,018.10