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	$243.73	12.148%	$273.3383	$273.34	$273.35	$273.30
Purchase #2	$51.71	4.217%	$53.8906	$53.89	$53.90	$53.90
Purchase #3	$108.63	11.619%	$121.2517	$121.25	$121.25	$121.30
Purchase #4	$233.75	13.300%	$264.8388	$264.84	$264.85	$264.80
Purchase #5	$221.54	4.760%	$232.0853	$232.09	$232.10	$232.10
Purchase #6	$71.95	9.638%	$78.8845	$78.88	$78.90	$78.90
Purchase #7	$248.41	11.758%	$277.618	$277.62	$277.60	$277.60
7 purchase totals =	$1,179.72		$1,301.9072	$1,301.91	$1,301.95	$1,301.90