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	$165.33	12.868%	$186.6047	$186.60	$186.60	$186.60
Purchase #2	$101.25	3.826%	$105.1238	$105.12	$105.10	$105.10
Purchase #3	$82.93	10.790%	$91.8781	$91.88	$91.90	$91.90
Purchase #4	$41.96	10.640%	$46.4245	$46.42	$46.40	$46.40
Purchase #5	$86.89	10.537%	$96.0456	$96.05	$96.05	$96.00
Purchase #6	$35.28	5.488%	$37.2162	$37.22	$37.20	$37.20
Purchase #7	$84.71	11.593%	$94.5304	$94.53	$94.55	$94.50
7 purchase totals =	$598.35		$657.8233	$657.82	$657.80	$657.70