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	$27.86	12.220%	$31.2645	$31.26	$31.25	$31.30
Purchase #2	$153.45	9.817%	$168.5142	$168.51	$168.50	$168.50
Purchase #3	$37.36	13.822%	$42.5239	$42.52	$42.50	$42.50
Purchase #4	$103.95	10.557%	$114.924	$114.92	$114.90	$114.90
Purchase #5	$177.76	13.337%	$201.4679	$201.47	$201.45	$201.50
Purchase #6	$200.58	9.316%	$219.266	$219.27	$219.25	$219.30
Purchase #7	$69.34	10.279%	$76.4675	$76.47	$76.45	$76.50
7 purchase totals =	$770.30		$854.4280	$854.42	$854.30	$854.50