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	$59.66	5.618%	$63.0117	$63.01	$63.00	$63.00
Purchase #2	$50.49	3.438%	$52.2258	$52.23	$52.25	$52.20
Purchase #3	$100.37	9.470%	$109.875	$109.88	$109.90	$109.90
Purchase #4	$94.66	11.654%	$105.6917	$105.69	$105.70	$105.70
Purchase #5	$225.48	6.688%	$240.5601	$240.56	$240.55	$240.60
Purchase #6	$112.27	8.357%	$121.6524	$121.65	$121.65	$121.70
Purchase #7	$94.83	5.735%	$100.2685	$100.27	$100.25	$100.30
7 purchase totals =	$737.76		$793.2852	$793.29	$793.30	$793.40