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	$138.72	6.134%	$147.2291	$147.23	$147.25	$147.20
Purchase #2	$209.94	8.759%	$228.3286	$228.33	$228.35	$228.30
Purchase #3	$148.93	4.425%	$155.5202	$155.52	$155.50	$155.50
Purchase #4	$36.89	4.784%	$38.6548	$38.65	$38.65	$38.70
Purchase #5	$141.37	13.800%	$160.8791	$160.88	$160.90	$160.90
Purchase #6	$247.47	8.353%	$268.1412	$268.14	$268.15	$268.10
Purchase #7	$146.59	6.578%	$156.2327	$156.23	$156.25	$156.20
7 purchase totals =	$1,069.91		$1,154.9857	$1,154.98	$1,155.05	$1,154.90