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	$30.56	4.664%	$31.9853	$31.99	$32.00	$32.00
Purchase #2	$110.59	4.240%	$115.279	$115.28	$115.30	$115.30
Purchase #3	$134.32	13.492%	$152.4425	$152.44	$152.45	$152.40
Purchase #4	$221.67	13.482%	$251.5555	$251.56	$251.55	$251.60
Purchase #5	$40.35	10.287%	$44.5008	$44.50	$44.50	$44.50
Purchase #6	$53.47	5.529%	$56.4264	$56.43	$56.45	$56.40
Purchase #7	$81.53	11.464%	$90.8766	$90.88	$90.90	$90.90
7 purchase totals =	$672.49		$743.0661	$743.08	$743.15	$743.10