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	$100.46	9.264%	$109.7666	$109.77	$109.75	$109.80
Purchase #2	$144.72	6.273%	$153.7983	$153.80	$153.80	$153.80
Purchase #3	$169.76	9.439%	$185.7836	$185.78	$185.80	$185.80
Purchase #4	$102.69	8.578%	$111.4987	$111.50	$111.50	$111.50
Purchase #5	$68.69	7.383%	$73.7614	$73.76	$73.75	$73.80
Purchase #6	$125.42	13.207%	$141.9842	$141.98	$142.00	$142.00
Purchase #7	$5.56	13.554%	$6.3136	$6.31	$6.30	$6.30
7 purchase totals =	$717.30		$782.9064	$782.90	$782.90	$783.00