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	$71.48	3.448%	$73.9446	$73.94	$73.95	$73.90
Purchase #2	$140.48	7.217%	$150.6184	$150.62	$150.60	$150.60
Purchase #3	$94.51	10.471%	$104.4061	$104.41	$104.40	$104.40
Purchase #4	$250.98	7.511%	$269.8311	$269.83	$269.85	$269.80
Purchase #5	$30.38	9.546%	$33.2801	$33.28	$33.30	$33.30
Purchase #6	$92.63	6.140%	$98.3175	$98.32	$98.30	$98.30
Purchase #7	$233.25	6.498%	$248.4066	$248.41	$248.40	$248.40
7 purchase totals =	$913.71		$978.8044	$978.81	$978.80	$978.70