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	$36.55	3.194%	$37.7174	$37.72	$37.70	$37.70
Purchase #2	$239.60	11.795%	$267.8608	$267.86	$267.85	$267.90
Purchase #3	$86.53	3.271%	$89.3604	$89.36	$89.35	$89.40
Purchase #4	$87.48	7.600%	$94.1285	$94.13	$94.15	$94.10
Purchase #5	$116.62	3.218%	$120.3728	$120.37	$120.35	$120.40
Purchase #6	$158.98	12.435%	$178.7492	$178.75	$178.75	$178.70
Purchase #7	$80.59	6.528%	$85.8509	$85.85	$85.85	$85.90
7 purchase totals =	$806.35		$874.0400	$874.04	$874.00	$874.10