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	$108.50	6.518%	$115.572	$115.57	$115.55	$115.60
Purchase #2	$175.47	11.797%	$196.1702	$196.17	$196.15	$196.20
Purchase #3	$69.48	11.494%	$77.466	$77.47	$77.45	$77.50
Purchase #4	$186.53	3.216%	$192.5288	$192.53	$192.55	$192.50
Purchase #5	$68.78	6.621%	$73.3339	$73.33	$73.35	$73.30
Purchase #6	$32.50	8.737%	$35.3395	$35.34	$35.35	$35.30
Purchase #7	$48.25	10.816%	$53.4687	$53.47	$53.45	$53.50
7 purchase totals =	$689.51		$743.8791	$743.88	$743.85	$743.90