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	$51.41	10.779%	$56.9515	$56.95	$56.95	$57.00
Purchase #2	$22.48	12.428%	$25.2738	$25.27	$25.25	$25.30
Purchase #3	$77.47	8.242%	$83.8551	$83.86	$83.85	$83.90
Purchase #4	$38.39	9.591%	$42.072	$42.07	$42.05	$42.10
Purchase #5	$150.27	6.629%	$160.2314	$160.23	$160.25	$160.20
Purchase #6	$100.33	3.228%	$103.5687	$103.57	$103.55	$103.60
Purchase #7	$27.94	9.362%	$30.5557	$30.56	$30.55	$30.60
7 purchase totals =	$468.29		$502.5082	$502.51	$502.45	$502.70