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	$77.28	4.436%	$80.7081	$80.71	$80.70	$80.70
Purchase #2	$159.74	13.521%	$181.3384	$181.34	$181.35	$181.30
Purchase #3	$25.52	6.469%	$27.1709	$27.17	$27.15	$27.20
Purchase #4	$201.33	3.275%	$207.9236	$207.92	$207.90	$207.90
Purchase #5	$200.33	7.698%	$215.7514	$215.75	$215.75	$215.80
Purchase #6	$83.89	6.693%	$89.5048	$89.50	$89.50	$89.50
Purchase #7	$135.70	3.227%	$140.079	$140.08	$140.10	$140.10
7 purchase totals =	$883.79		$942.4762	$942.47	$942.45	$942.50