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	$36.48	10.396%	$40.2725	$40.27	$40.25	$40.30
Purchase #2	$211.46	10.301%	$233.2425	$233.24	$233.25	$233.20
Purchase #3	$57.86	9.789%	$63.5239	$63.52	$63.50	$63.50
Purchase #4	$33.33	7.227%	$35.7388	$35.74	$35.75	$35.70
Purchase #5	$34.57	8.373%	$37.4645	$37.46	$37.45	$37.50
Purchase #6	$179.54	8.277%	$194.4005	$194.40	$194.40	$194.40
Purchase #7	$82.87	7.274%	$88.898	$88.90	$88.90	$88.90
7 purchase totals =	$636.11		$693.5407	$693.53	$693.50	$693.50