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	$223.34	11.231%	$248.4233	$248.42	$248.40	$248.40
Purchase #2	$129.27	13.573%	$146.8158	$146.82	$146.80	$146.80
Purchase #3	$9.53	9.406%	$10.4264	$10.43	$10.45	$10.40
Purchase #4	$128.86	8.630%	$139.9806	$139.98	$140.00	$140.00
Purchase #5	$193.50	6.413%	$205.9092	$205.91	$205.90	$205.90
Purchase #6	$166.49	11.120%	$185.0037	$185.00	$185.00	$185.00
Purchase #7	$55.34	8.235%	$59.8972	$59.90	$59.90	$59.90
7 purchase totals =	$906.33		$996.4562	$996.46	$996.45	$996.40