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	$76.34	3.339%	$78.889	$78.89	$78.90	$78.90
Purchase #2	$198.88	5.651%	$210.1187	$210.12	$210.10	$210.10
Purchase #3	$160.95	8.695%	$174.9446	$174.94	$174.95	$174.90
Purchase #4	$26.64	5.594%	$28.1302	$28.13	$28.15	$28.10
Purchase #5	$138.71	6.788%	$148.1256	$148.13	$148.15	$148.10
Purchase #6	$240.94	12.376%	$270.7587	$270.76	$270.75	$270.80
Purchase #7	$49.92	5.240%	$52.5358	$52.54	$52.55	$52.50
7 purchase totals =	$892.38		$963.5026	$963.51	$963.55	$963.40