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	$178.79	4.681%	$187.1592	$187.16	$187.15	$187.20
Purchase #2	$51.59	13.347%	$58.4757	$58.48	$58.50	$58.50
Purchase #3	$24.47	10.476%	$27.0335	$27.03	$27.05	$27.00
Purchase #4	$73.87	7.496%	$79.4073	$79.41	$79.40	$79.40
Purchase #5	$43.96	5.153%	$46.2253	$46.23	$46.25	$46.20
Purchase #6	$82.34	10.447%	$90.9421	$90.94	$90.95	$90.90
Purchase #7	$65.28	3.617%	$67.6412	$67.64	$67.65	$67.60
7 purchase totals =	$520.30		$556.8843	$556.89	$556.95	$556.80