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	$86.36	5.280%	$90.9198	$90.92	$90.90	$90.90
Purchase #2	$123.29	8.139%	$133.3246	$133.32	$133.30	$133.30
Purchase #3	$24.76	6.812%	$26.4467	$26.45	$26.45	$26.40
Purchase #4	$30.79	8.308%	$33.348	$33.35	$33.35	$33.30
Purchase #5	$89.27	10.133%	$98.3157	$98.32	$98.30	$98.30
Purchase #6	$210.79	6.152%	$223.7578	$223.76	$223.75	$223.80
Purchase #7	$80.94	7.720%	$87.1886	$87.19	$87.20	$87.20
7 purchase totals =	$646.20		$693.3012	$693.31	$693.25	$693.20