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	$250.50	5.437%	$264.1197	$264.12	$264.10	$264.10
Purchase #2	$104.82	6.744%	$111.8891	$111.89	$111.90	$111.90
Purchase #3	$81.98	8.526%	$88.9696	$88.97	$88.95	$89.00
Purchase #4	$24.36	12.290%	$27.3538	$27.35	$27.35	$27.40
Purchase #5	$167.66	11.596%	$187.1019	$187.10	$187.10	$187.10
Purchase #6	$177.63	6.107%	$188.4779	$188.48	$188.50	$188.50
Purchase #7	$20.92	3.315%	$21.6135	$21.61	$21.60	$21.60
7 purchase totals =	$827.87		$889.5255	$889.52	$889.50	$889.60