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	$227.39	11.612%	$253.7945	$253.79	$253.80	$253.80
Purchase #2	$97.69	11.755%	$109.1735	$109.17	$109.15	$109.20
Purchase #3	$133.63	6.250%	$141.9819	$141.98	$142.00	$142.00
Purchase #4	$63.50	11.115%	$70.558	$70.56	$70.55	$70.60
Purchase #5	$97.29	4.334%	$101.5065	$101.51	$101.50	$101.50
Purchase #6	$64.55	12.306%	$72.4935	$72.49	$72.50	$72.50
Purchase #7	$91.46	9.645%	$100.2813	$100.28	$100.30	$100.30
7 purchase totals =	$775.51		$849.7892	$849.78	$849.80	$849.90