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	$145.98	6.263%	$155.1227	$155.12	$155.10	$155.10
Purchase #2	$55.70	7.150%	$59.6826	$59.68	$59.70	$59.70
Purchase #3	$82.32	9.213%	$89.9041	$89.90	$89.90	$89.90
Purchase #4	$235.58	10.448%	$260.1934	$260.19	$260.20	$260.20
Purchase #5	$23.35	10.701%	$25.8487	$25.85	$25.85	$25.80
Purchase #6	$165.44	5.121%	$173.9122	$173.91	$173.90	$173.90
Purchase #7	$219.31	11.784%	$245.1535	$245.15	$245.15	$245.20
7 purchase totals =	$927.68		$1,009.8172	$1,009.80	$1,009.80	$1,009.80