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	$110.61	7.445%	$118.8449	$118.84	$118.85	$118.80
Purchase #2	$210.28	4.111%	$218.9246	$218.92	$218.90	$218.90
Purchase #3	$115.69	10.119%	$127.3967	$127.40	$127.40	$127.40
Purchase #4	$196.62	6.541%	$209.4809	$209.48	$209.50	$209.50
Purchase #5	$161.67	11.815%	$180.7713	$180.77	$180.75	$180.80
Purchase #6	$123.31	6.140%	$130.8812	$130.88	$130.90	$130.90
Purchase #7	$181.43	12.526%	$204.1559	$204.16	$204.15	$204.20
7 purchase totals =	$1,099.61		$1,190.4555	$1,190.45	$1,190.45	$1,190.50