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	$106.73	8.275%	$115.5619	$115.56	$115.55	$115.60
Purchase #2	$45.65	11.398%	$50.8532	$50.85	$50.85	$50.90
Purchase #3	$37.35	8.577%	$40.5535	$40.55	$40.55	$40.60
Purchase #4	$125.45	5.123%	$131.8768	$131.88	$131.90	$131.90
Purchase #5	$178.50	6.361%	$189.8544	$189.85	$189.85	$189.90
Purchase #6	$229.61	10.463%	$253.6341	$253.63	$253.65	$253.60
Purchase #7	$167.92	6.375%	$178.6249	$178.62	$178.60	$178.60
7 purchase totals =	$891.21		$960.9588	$960.94	$960.95	$961.10