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	$94.63	4.589%	$98.9726	$98.97	$98.95	$99.00
Purchase #2	$112.84	7.122%	$120.8765	$120.88	$120.90	$120.90
Purchase #3	$147.69	12.385%	$165.9814	$165.98	$166.00	$166.00
Purchase #4	$105.62	6.554%	$112.5423	$112.54	$112.55	$112.50
Purchase #5	$169.33	12.868%	$191.1194	$191.12	$191.10	$191.10
Purchase #6	$105.44	7.528%	$113.3775	$113.38	$113.40	$113.40
Purchase #7	$56.83	8.478%	$61.648	$61.65	$61.65	$61.60
7 purchase totals =	$792.38		$864.5177	$864.52	$864.55	$864.50