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	$220.96	8.819%	$240.4465	$240.45	$240.45	$240.40
Purchase #2	$61.49	5.280%	$64.7367	$64.74	$64.75	$64.70
Purchase #3	$122.31	7.342%	$131.29	$131.29	$131.30	$131.30
Purchase #4	$92.80	7.120%	$99.4074	$99.41	$99.40	$99.40
Purchase #5	$114.34	10.765%	$126.6487	$126.65	$126.65	$126.60
Purchase #6	$31.52	6.635%	$33.6114	$33.61	$33.60	$33.60
Purchase #7	$147.44	8.744%	$160.3322	$160.33	$160.35	$160.30
7 purchase totals =	$790.86		$856.4729	$856.48	$856.50	$856.30