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	$84.35	10.608%	$93.2978	$93.30	$93.30	$93.30
Purchase #2	$93.70	6.763%	$100.0369	$100.04	$100.05	$100.00
Purchase #3	$33.94	9.130%	$37.0387	$37.04	$37.05	$37.00
Purchase #4	$30.63	10.520%	$33.8523	$33.85	$33.85	$33.90
Purchase #5	$90.76	5.783%	$96.0087	$96.01	$96.00	$96.00
Purchase #6	$69.52	6.226%	$73.8483	$73.85	$73.85	$73.80
Purchase #7	$72.83	9.184%	$79.5187	$79.52	$79.50	$79.50
7 purchase totals =	$475.73		$513.6014	$513.61	$513.60	$513.50