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	$93.48	7.148%	$100.162	$100.16	$100.15	$100.20
Purchase #2	$72.93	13.302%	$82.6311	$82.63	$82.65	$82.60
Purchase #3	$180.82	4.297%	$188.5898	$188.59	$188.60	$188.60
Purchase #4	$110.83	9.390%	$121.2369	$121.24	$121.25	$121.20
Purchase #5	$223.71	7.476%	$240.4346	$240.43	$240.45	$240.40
Purchase #6	$123.74	13.493%	$140.4362	$140.44	$140.45	$140.40
Purchase #7	$81.45	12.698%	$91.7925	$91.79	$91.80	$91.80
7 purchase totals =	$886.96		$965.2831	$965.28	$965.35	$965.20