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	$155.48	10.737%	$172.1739	$172.17	$172.15	$172.20
Purchase #2	$82.59	7.869%	$89.089	$89.09	$89.10	$89.10
Purchase #3	$163.75	11.373%	$182.3733	$182.37	$182.35	$182.40
Purchase #4	$94.86	5.165%	$99.7595	$99.76	$99.75	$99.80
Purchase #5	$196.84	11.453%	$219.3841	$219.38	$219.40	$219.40
Purchase #6	$25.75	8.146%	$27.8476	$27.85	$27.85	$27.80
Purchase #7	$63.38	12.658%	$71.4026	$71.40	$71.40	$71.40
7 purchase totals =	$782.65		$862.0300	$862.02	$862.00	$862.10