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	$46.38	13.204%	$52.504	$52.50	$52.50	$52.50
Purchase #2	$32.30	12.383%	$36.2997	$36.30	$36.30	$36.30
Purchase #3	$116.70	6.703%	$124.5224	$124.52	$124.50	$124.50
Purchase #4	$36.50	12.107%	$40.9191	$40.92	$40.90	$40.90
Purchase #5	$90.50	7.736%	$97.5011	$97.50	$97.50	$97.50
Purchase #6	$147.97	13.750%	$168.3159	$168.32	$168.30	$168.30
Purchase #7	$101.99	8.348%	$110.5041	$110.50	$110.50	$110.50
7 purchase totals =	$572.34		$630.5663	$630.56	$630.50	$630.50