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	$27.90	9.410%	$30.5254	$30.53	$30.55	$30.50
Purchase #2	$89.57	11.712%	$100.0604	$100.06	$100.05	$100.10
Purchase #3	$225.31	7.643%	$242.5304	$242.53	$242.55	$242.50
Purchase #4	$80.41	7.695%	$86.5975	$86.60	$86.60	$86.60
Purchase #5	$192.82	13.374%	$218.6077	$218.61	$218.60	$218.60
Purchase #6	$237.40	11.531%	$264.7746	$264.77	$264.75	$264.80
Purchase #7	$210.29	7.605%	$226.2826	$226.28	$226.30	$226.30
7 purchase totals =	$1,063.70		$1,169.3786	$1,169.38	$1,169.40	$1,169.40