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	$221.73	8.513%	$240.6059	$240.61	$240.60	$240.60
Purchase #2	$52.72	11.573%	$58.8213	$58.82	$58.80	$58.80
Purchase #3	$144.49	4.124%	$150.4488	$150.45	$150.45	$150.40
Purchase #4	$232.84	13.761%	$264.8811	$264.88	$264.90	$264.90
Purchase #5	$6.98	6.782%	$7.4534	$7.45	$7.45	$7.50
Purchase #6	$78.48	5.774%	$83.0114	$83.01	$83.00	$83.00
Purchase #7	$28.64	6.330%	$30.4529	$30.45	$30.45	$30.50
7 purchase totals =	$765.88		$835.6748	$835.67	$835.65	$835.70