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	$29.61	9.663%	$32.4712	$32.47	$32.45	$32.50
Purchase #2	$86.39	9.411%	$94.5202	$94.52	$94.50	$94.50
Purchase #3	$57.53	11.404%	$64.0907	$64.09	$64.10	$64.10
Purchase #4	$195.35	10.856%	$216.5572	$216.56	$216.55	$216.60
Purchase #5	$189.77	13.356%	$215.1157	$215.12	$215.10	$215.10
Purchase #6	$189.59	11.496%	$211.3853	$211.39	$211.40	$211.40
Purchase #7	$150.69	10.223%	$166.095	$166.10	$166.10	$166.10
7 purchase totals =	$898.93		$1,000.2353	$1,000.25	$1,000.20	$1,000.30