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	$32.36	10.816%	$35.8601	$35.86	$35.85	$35.90
Purchase #2	$121.92	12.812%	$137.5404	$137.54	$137.55	$137.50
Purchase #3	$148.48	13.792%	$168.9584	$168.96	$168.95	$169.00
Purchase #4	$188.34	5.201%	$198.1356	$198.14	$198.15	$198.10
Purchase #5	$58.39	8.568%	$63.3929	$63.39	$63.40	$63.40
Purchase #6	$43.91	8.206%	$47.5133	$47.51	$47.50	$47.50
Purchase #7	$37.33	7.489%	$40.1256	$40.13	$40.15	$40.10
7 purchase totals =	$630.73		$691.5263	$691.53	$691.55	$691.50