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	$100.46	9.403%	$109.9063	$109.91	$109.90	$109.90
Purchase #2	$135.39	5.391%	$142.6889	$142.69	$142.70	$142.70
Purchase #3	$81.97	4.312%	$85.5045	$85.50	$85.50	$85.50
Purchase #4	$55.47	11.658%	$61.9367	$61.94	$61.95	$61.90
Purchase #5	$46.61	6.109%	$49.4574	$49.46	$49.45	$49.50
Purchase #6	$243.64	8.867%	$265.2436	$265.24	$265.25	$265.20
Purchase #7	$187.79	5.807%	$198.695	$198.70	$198.70	$198.70
7 purchase totals =	$851.33		$913.4324	$913.44	$913.45	$913.40