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	$181.44	3.780%	$188.2984	$188.30	$188.30	$188.30
Purchase #2	$222.81	9.339%	$243.6182	$243.62	$243.60	$243.60
Purchase #3	$103.62	4.392%	$108.171	$108.17	$108.15	$108.20
Purchase #4	$27.56	12.771%	$31.0797	$31.08	$31.10	$31.10
Purchase #5	$116.56	7.325%	$125.098	$125.10	$125.10	$125.10
Purchase #6	$81.27	10.611%	$89.8936	$89.89	$89.90	$89.90
Purchase #7	$19.50	4.686%	$20.4138	$20.41	$20.40	$20.40
7 purchase totals =	$752.76		$806.5727	$806.57	$806.55	$806.60