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	$106.80	3.188%	$110.2048	$110.20	$110.20	$110.20
Purchase #2	$55.79	5.781%	$59.0152	$59.02	$59.00	$59.00
Purchase #3	$168.98	11.486%	$188.389	$188.39	$188.40	$188.40
Purchase #4	$88.88	10.421%	$98.1422	$98.14	$98.15	$98.10
Purchase #5	$173.66	5.734%	$183.6177	$183.62	$183.60	$183.60
Purchase #6	$81.63	10.308%	$90.0444	$90.04	$90.05	$90.00
Purchase #7	$103.92	5.712%	$109.8559	$109.86	$109.85	$109.90
7 purchase totals =	$779.66		$839.2692	$839.27	$839.25	$839.20