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	$30.49	3.151%	$31.4507	$31.45	$31.45	$31.50
Purchase #2	$243.54	10.690%	$269.5744	$269.57	$269.55	$269.60
Purchase #3	$54.31	9.498%	$59.4684	$59.47	$59.45	$59.50
Purchase #4	$83.68	5.624%	$88.3862	$88.39	$88.40	$88.40
Purchase #5	$78.41	5.125%	$82.4285	$82.43	$82.45	$82.40
Purchase #6	$77.30	7.119%	$82.803	$82.80	$82.80	$82.80
Purchase #7	$175.59	10.414%	$193.8759	$193.88	$193.90	$193.90
7 purchase totals =	$743.32		$807.9871	$807.99	$808.00	$808.10