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	$26.42	5.526%	$27.88	$27.88	$27.90	$27.90
Purchase #2	$105.97	12.122%	$118.8157	$118.82	$118.80	$118.80
Purchase #3	$96.29	6.623%	$102.6673	$102.67	$102.65	$102.70
Purchase #4	$25.88	11.170%	$28.7708	$28.77	$28.75	$28.80
Purchase #5	$100.73	11.562%	$112.3764	$112.38	$112.40	$112.40
Purchase #6	$40.57	3.833%	$42.125	$42.13	$42.15	$42.10
Purchase #7	$55.64	10.221%	$61.327	$61.33	$61.35	$61.30
7 purchase totals =	$451.50		$493.9622	$493.98	$494.00	$494.00