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	$248.50	8.872%	$270.5469	$270.55	$270.55	$270.50
Purchase #2	$169.63	10.682%	$187.7499	$187.75	$187.75	$187.70
Purchase #3	$128.65	13.801%	$146.405	$146.41	$146.40	$146.40
Purchase #4	$159.74	5.504%	$168.5321	$168.53	$168.55	$168.50
Purchase #5	$214.99	13.389%	$243.775	$243.78	$243.80	$243.80
Purchase #6	$98.41	11.654%	$109.8787	$109.88	$109.90	$109.90
Purchase #7	$89.98	9.722%	$98.7279	$98.73	$98.75	$98.70
7 purchase totals =	$1,109.90		$1,225.6155	$1,225.63	$1,225.70	$1,225.50