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	$180.92	6.394%	$192.488	$192.49	$192.50	$192.50
Purchase #2	$83.98	6.568%	$89.4958	$89.50	$89.50	$89.50
Purchase #3	$174.69	9.469%	$191.2314	$191.23	$191.25	$191.20
Purchase #4	$53.34	11.391%	$59.416	$59.42	$59.40	$59.40
Purchase #5	$110.87	5.107%	$116.5321	$116.53	$116.55	$116.50
Purchase #6	$75.82	6.557%	$80.7915	$80.79	$80.80	$80.80
Purchase #7	$193.97	9.270%	$211.951	$211.95	$211.95	$212.00
7 purchase totals =	$873.59		$941.9058	$941.91	$941.95	$941.90