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	$148.77	7.356%	$159.7135	$159.71	$159.70	$159.70
Purchase #2	$25.89	5.856%	$27.4061	$27.41	$27.40	$27.40
Purchase #3	$115.96	8.869%	$126.2445	$126.24	$126.25	$126.20
Purchase #4	$37.89	11.535%	$42.2606	$42.26	$42.25	$42.30
Purchase #5	$76.82	11.300%	$85.5007	$85.50	$85.50	$85.50
Purchase #6	$35.66	7.735%	$38.4183	$38.42	$38.40	$38.40
Purchase #7	$14.63	4.814%	$15.3343	$15.33	$15.35	$15.30
7 purchase totals =	$455.62		$494.8780	$494.87	$494.85	$494.80