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	$166.72	11.586%	$186.0362	$186.04	$186.05	$186.00
Purchase #2	$75.55	12.736%	$85.172	$85.17	$85.15	$85.20
Purchase #3	$93.34	5.828%	$98.7799	$98.78	$98.80	$98.80
Purchase #4	$144.56	4.337%	$150.8296	$150.83	$150.85	$150.80
Purchase #5	$72.81	6.453%	$77.5084	$77.51	$77.50	$77.50
Purchase #6	$140.34	3.244%	$144.8926	$144.89	$144.90	$144.90
Purchase #7	$250.31	13.396%	$283.8415	$283.84	$283.85	$283.80
7 purchase totals =	$943.63		$1,027.0602	$1,027.06	$1,027.10	$1,027.00