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	$55.37	11.238%	$61.5925	$61.59	$61.60	$61.60
Purchase #2	$136.40	9.169%	$148.9065	$148.91	$148.90	$148.90
Purchase #3	$165.82	11.573%	$185.0103	$185.01	$185.00	$185.00
Purchase #4	$58.83	6.287%	$62.5286	$62.53	$62.55	$62.50
Purchase #5	$135.41	3.132%	$139.651	$139.65	$139.65	$139.70
Purchase #6	$129.53	8.386%	$140.3924	$140.39	$140.40	$140.40
Purchase #7	$145.97	6.662%	$155.6945	$155.69	$155.70	$155.70
7 purchase totals =	$827.33		$893.7758	$893.77	$893.80	$893.80