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	$249.56	9.560%	$273.4179	$273.42	$273.40	$273.40
Purchase #2	$104.47	3.545%	$108.1735	$108.17	$108.15	$108.20
Purchase #3	$52.57	12.251%	$59.0104	$59.01	$59.00	$59.00
Purchase #4	$197.63	12.753%	$222.8338	$222.83	$222.85	$222.80
Purchase #5	$100.95	11.153%	$112.209	$112.21	$112.20	$112.20
Purchase #6	$163.61	12.588%	$184.2052	$184.21	$184.20	$184.20
Purchase #7	$82.48	3.637%	$85.4798	$85.48	$85.50	$85.50
7 purchase totals =	$951.27		$1,045.3296	$1,045.33	$1,045.30	$1,045.30