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	$89.84	11.116%	$99.8266	$99.83	$99.85	$99.80
Purchase #2	$243.84	4.397%	$254.5616	$254.56	$254.55	$254.60
Purchase #3	$200.81	4.550%	$209.9469	$209.95	$209.95	$209.90
Purchase #4	$104.99	12.471%	$118.0833	$118.08	$118.10	$118.10
Purchase #5	$28.93	8.661%	$31.4356	$31.44	$31.45	$31.40
Purchase #6	$56.91	12.212%	$63.8598	$63.86	$63.85	$63.90
Purchase #7	$223.53	4.154%	$232.8154	$232.82	$232.80	$232.80
7 purchase totals =	$948.85		$1,010.5292	$1,010.54	$1,010.55	$1,010.50