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	$91.44	4.265%	$95.3399	$95.34	$95.35	$95.30
Purchase #2	$86.27	12.589%	$97.1305	$97.13	$97.15	$97.10
Purchase #3	$55.28	6.718%	$58.9937	$58.99	$59.00	$59.00
Purchase #4	$142.88	9.462%	$156.3993	$156.40	$156.40	$156.40
Purchase #5	$10.74	6.691%	$11.4586	$11.46	$11.45	$11.50
Purchase #6	$79.44	12.823%	$89.6266	$89.63	$89.65	$89.60
Purchase #7	$84.73	6.224%	$90.0036	$90.00	$90.00	$90.00
7 purchase totals =	$550.78		$598.9522	$598.95	$599.00	$598.90