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	$149.92	8.417%	$162.5388	$162.54	$162.55	$162.50
Purchase #2	$138.97	5.335%	$146.384	$146.38	$146.40	$146.40
Purchase #3	$246.99	9.443%	$270.3133	$270.31	$270.30	$270.30
Purchase #4	$36.60	11.847%	$40.936	$40.94	$40.95	$40.90
Purchase #5	$98.90	11.842%	$110.6117	$110.61	$110.60	$110.60
Purchase #6	$170.85	4.360%	$178.2991	$178.30	$178.30	$178.30
Purchase #7	$62.94	13.684%	$71.5527	$71.55	$71.55	$71.60
7 purchase totals =	$905.17		$980.6356	$980.63	$980.65	$980.60