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	$232.33	12.516%	$261.4084	$261.41	$261.40	$261.40
Purchase #2	$164.35	12.777%	$185.349	$185.35	$185.35	$185.30
Purchase #3	$52.92	10.506%	$58.4798	$58.48	$58.50	$58.50
Purchase #4	$73.54	13.382%	$83.3811	$83.38	$83.40	$83.40
Purchase #5	$153.26	11.668%	$171.1424	$171.14	$171.15	$171.10
Purchase #6	$19.84	12.188%	$22.2581	$22.26	$22.25	$22.30
Purchase #7	$81.52	9.484%	$89.2514	$89.25	$89.25	$89.30
7 purchase totals =	$777.76		$871.2702	$871.27	$871.30	$871.30