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	$42.57	8.804%	$46.3179	$46.32	$46.30	$46.30
Purchase #2	$172.99	12.320%	$194.3024	$194.30	$194.30	$194.30
Purchase #3	$131.81	7.750%	$142.0253	$142.03	$142.05	$142.00
Purchase #4	$35.79	5.837%	$37.8791	$37.88	$37.90	$37.90
Purchase #5	$110.72	11.361%	$123.2989	$123.30	$123.30	$123.30
Purchase #6	$175.53	9.844%	$192.8092	$192.81	$192.80	$192.80
Purchase #7	$30.98	8.798%	$33.7056	$33.71	$33.70	$33.70
7 purchase totals =	$700.39		$770.3384	$770.35	$770.35	$770.30