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	$189.46	4.443%	$197.8777	$197.88	$197.90	$197.90
Purchase #2	$107.61	11.870%	$120.3833	$120.38	$120.40	$120.40
Purchase #3	$88.48	11.758%	$98.8835	$98.88	$98.90	$98.90
Purchase #4	$238.90	13.668%	$271.5529	$271.55	$271.55	$271.60
Purchase #5	$223.59	13.166%	$253.0279	$253.03	$253.05	$253.00
Purchase #6	$78.46	3.230%	$80.9943	$80.99	$81.00	$81.00
Purchase #7	$57.75	6.705%	$61.6221	$61.62	$61.60	$61.60
7 purchase totals =	$984.25		$1,084.3417	$1,084.33	$1,084.40	$1,084.40