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	$55.68	3.621%	$57.6962	$57.70	$57.70	$57.70
Purchase #2	$190.78	3.422%	$197.3085	$197.31	$197.30	$197.30
Purchase #3	$190.52	12.271%	$213.8987	$213.90	$213.90	$213.90
Purchase #4	$180.27	11.464%	$200.9362	$200.94	$200.95	$200.90
Purchase #5	$96.71	3.568%	$100.1606	$100.16	$100.15	$100.20
Purchase #6	$77.93	7.763%	$83.9797	$83.98	$84.00	$84.00
Purchase #7	$180.90	8.535%	$196.3398	$196.34	$196.35	$196.30
7 purchase totals =	$972.79		$1,050.3197	$1,050.33	$1,050.35	$1,050.30