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	$69.77	12.426%	$78.4396	$78.44	$78.45	$78.40
Purchase #2	$98.29	5.833%	$104.0233	$104.02	$104.00	$104.00
Purchase #3	$185.96	12.559%	$209.3147	$209.31	$209.30	$209.30
Purchase #4	$46.61	9.498%	$51.037	$51.04	$51.05	$51.00
Purchase #5	$227.54	11.337%	$253.3362	$253.34	$253.35	$253.30
Purchase #6	$83.96	10.574%	$92.8379	$92.84	$92.85	$92.80
Purchase #7	$96.66	7.412%	$103.8244	$103.82	$103.80	$103.80
7 purchase totals =	$808.79		$892.8131	$892.81	$892.80	$892.60