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	$82.58	6.744%	$88.1492	$88.15	$88.15	$88.10
Purchase #2	$83.51	7.236%	$89.5528	$89.55	$89.55	$89.60
Purchase #3	$115.84	6.281%	$123.1159	$123.12	$123.10	$123.10
Purchase #4	$43.50	6.310%	$46.2449	$46.24	$46.25	$46.20
Purchase #5	$183.46	12.570%	$206.5209	$206.52	$206.50	$206.50
Purchase #6	$235.90	5.656%	$249.2425	$249.24	$249.25	$249.20
Purchase #7	$155.72	7.159%	$166.868	$166.87	$166.85	$166.90
7 purchase totals =	$900.51		$969.6942	$969.69	$969.65	$969.60