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	$152.43	9.602%	$167.0663	$167.07	$167.05	$167.10
Purchase #2	$57.36	6.524%	$61.1022	$61.10	$61.10	$61.10
Purchase #3	$60.67	8.738%	$65.9713	$65.97	$65.95	$66.00
Purchase #4	$50.34	13.570%	$57.1711	$57.17	$57.15	$57.20
Purchase #5	$82.39	11.468%	$91.8385	$91.84	$91.85	$91.80
Purchase #6	$200.86	10.841%	$222.6352	$222.64	$222.65	$222.60
Purchase #7	$245.36	11.576%	$273.7629	$273.76	$273.75	$273.80
7 purchase totals =	$849.41		$939.5475	$939.55	$939.50	$939.60