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	$160.98	6.399%	$171.2811	$171.28	$171.30	$171.30
Purchase #2	$53.51	6.371%	$56.9191	$56.92	$56.90	$56.90
Purchase #3	$106.96	10.609%	$118.3074	$118.31	$118.30	$118.30
Purchase #4	$105.72	12.352%	$118.7785	$118.78	$118.80	$118.80
Purchase #5	$205.56	3.451%	$212.6539	$212.65	$212.65	$212.70
Purchase #6	$165.50	12.320%	$185.8896	$185.89	$185.90	$185.90
Purchase #7	$218.90	11.203%	$243.4234	$243.42	$243.40	$243.40
7 purchase totals =	$1,017.13		$1,107.2530	$1,107.25	$1,107.25	$1,107.30