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	$97.72	3.682%	$101.3181	$101.32	$101.30	$101.30
Purchase #2	$181.83	10.201%	$200.3785	$200.38	$200.40	$200.40
Purchase #3	$18.39	10.800%	$20.3761	$20.38	$20.40	$20.40
Purchase #4	$120.34	8.509%	$130.5797	$130.58	$130.60	$130.60
Purchase #5	$37.45	10.517%	$41.3886	$41.39	$41.40	$41.40
Purchase #6	$214.90	6.625%	$229.1371	$229.14	$229.15	$229.10
Purchase #7	$114.28	9.502%	$125.1389	$125.14	$125.15	$125.10
7 purchase totals =	$784.91		$848.3170	$848.33	$848.40	$848.30