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	$85.44	5.663%	$90.2785	$90.28	$90.30	$90.30
Purchase #2	$249.84	13.779%	$284.2655	$284.27	$284.25	$284.30
Purchase #3	$31.27	3.362%	$32.3213	$32.32	$32.30	$32.30
Purchase #4	$49.87	11.744%	$55.7267	$55.73	$55.75	$55.70
Purchase #5	$190.62	11.740%	$212.9988	$213.00	$213.00	$213.00
Purchase #6	$27.89	8.645%	$30.3011	$30.30	$30.30	$30.30
Purchase #7	$39.33	3.394%	$40.6649	$40.66	$40.65	$40.70
7 purchase totals =	$674.26		$746.5568	$746.56	$746.55	$746.60