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	$106.49	11.595%	$118.8375	$118.84	$118.85	$118.80
Purchase #2	$56.78	4.422%	$59.2908	$59.29	$59.30	$59.30
Purchase #3	$140.85	5.365%	$148.4066	$148.41	$148.40	$148.40
Purchase #4	$119.91	3.314%	$123.8838	$123.88	$123.90	$123.90
Purchase #5	$78.69	11.805%	$87.9794	$87.98	$88.00	$88.00
Purchase #6	$221.25	8.728%	$240.5607	$240.56	$240.55	$240.60
Purchase #7	$240.33	13.858%	$273.6349	$273.63	$273.65	$273.60
7 purchase totals =	$964.30		$1,052.5937	$1,052.59	$1,052.65	$1,052.60