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	$156.90	8.278%	$169.8882	$169.89	$169.90	$169.90
Purchase #2	$92.61	6.263%	$98.4102	$98.41	$98.40	$98.40
Purchase #3	$175.99	11.642%	$196.4788	$196.48	$196.50	$196.50
Purchase #4	$233.69	6.368%	$248.5714	$248.57	$248.55	$248.60
Purchase #5	$69.46	11.435%	$77.4028	$77.40	$77.40	$77.40
Purchase #6	$121.45	9.424%	$132.8954	$132.90	$132.90	$132.90
Purchase #7	$73.97	3.296%	$76.4081	$76.41	$76.40	$76.40
7 purchase totals =	$924.07		$1,000.0549	$1,000.06	$1,000.05	$1,000.10