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	$209.86	6.603%	$223.7171	$223.72	$223.70	$223.70
Purchase #2	$79.66	12.134%	$89.3259	$89.33	$89.35	$89.30
Purchase #3	$75.59	8.441%	$81.9706	$81.97	$81.95	$82.00
Purchase #4	$16.28	6.253%	$17.298	$17.30	$17.30	$17.30
Purchase #5	$225.66	7.406%	$242.3724	$242.37	$242.35	$242.40
Purchase #6	$141.76	9.384%	$155.0628	$155.06	$155.05	$155.10
Purchase #7	$35.59	11.581%	$39.7117	$39.71	$39.70	$39.70
7 purchase totals =	$784.40		$849.4585	$849.46	$849.40	$849.50