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	$91.80	3.780%	$95.27	$95.27	$95.25	$95.30
Purchase #2	$67.72	6.661%	$72.2308	$72.23	$72.25	$72.20
Purchase #3	$123.91	9.793%	$136.0445	$136.04	$136.05	$136.00
Purchase #4	$62.94	3.743%	$65.2958	$65.30	$65.30	$65.30
Purchase #5	$107.44	6.746%	$114.6879	$114.69	$114.70	$114.70
Purchase #6	$126.82	11.424%	$141.3079	$141.31	$141.30	$141.30
Purchase #7	$14.70	4.311%	$15.3337	$15.33	$15.35	$15.30
7 purchase totals =	$595.33		$640.1706	$640.17	$640.20	$640.10