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	$213.73	9.446%	$233.9189	$233.92	$233.90	$233.90
Purchase #2	$108.53	9.552%	$118.8968	$118.90	$118.90	$118.90
Purchase #3	$91.61	12.600%	$103.1529	$103.15	$103.15	$103.20
Purchase #4	$87.96	9.258%	$96.1033	$96.10	$96.10	$96.10
Purchase #5	$83.57	6.562%	$89.0539	$89.05	$89.05	$89.10
Purchase #6	$73.50	12.781%	$82.894	$82.89	$82.90	$82.90
Purchase #7	$156.69	12.142%	$175.7153	$175.72	$175.70	$175.70
7 purchase totals =	$815.59		$899.7351	$899.73	$899.70	$899.80