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	$79.83	13.483%	$90.5935	$90.59	$90.60	$90.60
Purchase #2	$80.99	11.501%	$90.3047	$90.30	$90.30	$90.30
Purchase #3	$140.87	4.378%	$147.0373	$147.04	$147.05	$147.00
Purchase #4	$121.33	8.596%	$131.7595	$131.76	$131.75	$131.80
Purchase #5	$26.96	13.246%	$30.5311	$30.53	$30.55	$30.50
Purchase #6	$131.95	10.112%	$145.2928	$145.29	$145.30	$145.30
Purchase #7	$168.61	13.854%	$191.9692	$191.97	$191.95	$192.00
7 purchase totals =	$750.54		$827.4881	$827.48	$827.50	$827.50