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	$25.45	13.491%	$28.8835	$28.88	$28.90	$28.90
Purchase #2	$115.28	10.459%	$127.3371	$127.34	$127.35	$127.30
Purchase #3	$225.51	12.700%	$254.1498	$254.15	$254.15	$254.10
Purchase #4	$214.94	6.712%	$229.3668	$229.37	$229.35	$229.40
Purchase #5	$98.33	5.152%	$103.396	$103.40	$103.40	$103.40
Purchase #6	$169.93	12.615%	$191.3667	$191.37	$191.35	$191.40
Purchase #7	$7.71	7.740%	$8.3068	$8.31	$8.30	$8.30
7 purchase totals =	$857.15		$942.8067	$942.82	$942.80	$942.80