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	$86.34	3.488%	$89.3515	$89.35	$89.35	$89.40
Purchase #2	$71.29	6.647%	$76.0286	$76.03	$76.05	$76.00
Purchase #3	$73.50	6.153%	$78.0225	$78.02	$78.00	$78.00
Purchase #4	$210.68	13.776%	$239.7033	$239.70	$239.70	$239.70
Purchase #5	$131.68	8.428%	$142.778	$142.78	$142.80	$142.80
Purchase #6	$142.59	6.525%	$151.894	$151.89	$151.90	$151.90
Purchase #7	$131.97	10.297%	$145.559	$145.56	$145.55	$145.60
7 purchase totals =	$848.05		$923.3369	$923.33	$923.35	$923.40