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	$29.50	9.597%	$32.3311	$32.33	$32.35	$32.30
Purchase #2	$29.71	8.129%	$32.1251	$32.13	$32.15	$32.10
Purchase #3	$229.57	8.558%	$249.2166	$249.22	$249.20	$249.20
Purchase #4	$40.77	12.535%	$45.8805	$45.88	$45.90	$45.90
Purchase #5	$51.86	10.327%	$57.2156	$57.22	$57.20	$57.20
Purchase #6	$134.73	9.196%	$147.1198	$147.12	$147.10	$147.10
Purchase #7	$150.40	12.467%	$169.1504	$169.15	$169.15	$169.20
7 purchase totals =	$666.54		$733.0391	$733.05	$733.05	$733.00