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	$53.74	3.354%	$55.5424	$55.54	$55.55	$55.50
Purchase #2	$88.62	12.637%	$99.8189	$99.82	$99.80	$99.80
Purchase #3	$87.74	8.729%	$95.3988	$95.40	$95.40	$95.40
Purchase #4	$30.42	11.109%	$33.7994	$33.80	$33.80	$33.80
Purchase #5	$145.44	4.193%	$151.5383	$151.54	$151.55	$151.50
Purchase #6	$24.61	3.438%	$25.4561	$25.46	$25.45	$25.50
Purchase #7	$131.98	11.554%	$147.229	$147.23	$147.25	$147.20
7 purchase totals =	$562.55		$608.7829	$608.79	$608.80	$608.70