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	$28.76	8.693%	$31.2601	$31.26	$31.25	$31.30
Purchase #2	$90.57	6.321%	$96.2949	$96.29	$96.30	$96.30
Purchase #3	$134.36	12.582%	$151.2652	$151.27	$151.25	$151.30
Purchase #4	$247.98	9.563%	$271.6943	$271.69	$271.70	$271.70
Purchase #5	$170.83	8.450%	$185.2651	$185.27	$185.25	$185.30
Purchase #6	$213.97	6.360%	$227.5785	$227.58	$227.60	$227.60
Purchase #7	$30.70	6.732%	$32.7667	$32.77	$32.75	$32.80
7 purchase totals =	$917.17		$996.1248	$996.13	$996.10	$996.30