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	$249.92	3.512%	$258.6972	$258.70	$258.70	$258.70
Purchase #2	$88.69	3.608%	$91.8899	$91.89	$91.90	$91.90
Purchase #3	$152.28	12.293%	$170.9998	$171.00	$171.00	$171.00
Purchase #4	$98.63	11.391%	$109.8649	$109.86	$109.85	$109.90
Purchase #5	$246.60	9.825%	$270.8285	$270.83	$270.85	$270.80
Purchase #6	$28.92	13.578%	$32.8468	$32.85	$32.85	$32.80
Purchase #7	$59.89	8.396%	$64.9184	$64.92	$64.90	$64.90
7 purchase totals =	$924.93		$1,000.0455	$1,000.05	$1,000.05	$1,000.00