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	$9.40	6.851%	$10.044	$10.04	$10.05	$10.00
Purchase #2	$31.43	4.147%	$32.7334	$32.73	$32.75	$32.70
Purchase #3	$225.54	10.108%	$248.3376	$248.34	$248.35	$248.30
Purchase #4	$165.33	3.771%	$171.5646	$171.56	$171.55	$171.60
Purchase #5	$125.84	7.186%	$134.8829	$134.88	$134.90	$134.90
Purchase #6	$114.97	11.609%	$128.3169	$128.32	$128.30	$128.30
Purchase #7	$119.52	10.302%	$131.833	$131.83	$131.85	$131.80
7 purchase totals =	$792.03		$857.7124	$857.70	$857.75	$857.60