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	$66.89	9.480%	$73.2312	$73.23	$73.25	$73.20
Purchase #2	$159.96	7.477%	$171.9202	$171.92	$171.90	$171.90
Purchase #3	$39.49	6.365%	$42.0035	$42.00	$42.00	$42.00
Purchase #4	$74.89	11.872%	$83.7809	$83.78	$83.80	$83.80
Purchase #5	$250.52	13.272%	$283.769	$283.77	$283.75	$283.80
Purchase #6	$180.85	8.386%	$196.0161	$196.02	$196.00	$196.00
Purchase #7	$216.31	4.447%	$225.9293	$225.93	$225.95	$225.90
7 purchase totals =	$988.91		$1,076.6502	$1,076.65	$1,076.65	$1,076.60