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	$38.67	5.780%	$40.9051	$40.91	$40.90	$40.90
Purchase #2	$57.42	5.377%	$60.5075	$60.51	$60.50	$60.50
Purchase #3	$124.44	12.275%	$139.715	$139.72	$139.70	$139.70
Purchase #4	$189.87	4.705%	$198.8034	$198.80	$198.80	$198.80
Purchase #5	$53.85	9.695%	$59.0708	$59.07	$59.05	$59.10
Purchase #6	$55.35	4.591%	$57.8911	$57.89	$57.90	$57.90
Purchase #7	$247.67	9.352%	$270.8321	$270.83	$270.85	$270.80
7 purchase totals =	$767.27		$827.7250	$827.73	$827.70	$827.70