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	$173.67	8.836%	$189.0155	$189.02	$189.00	$189.00
Purchase #2	$72.88	11.499%	$81.2605	$81.26	$81.25	$81.30
Purchase #3	$78.44	5.564%	$82.8044	$82.80	$82.80	$82.80
Purchase #4	$166.63	13.421%	$188.9934	$188.99	$189.00	$189.00
Purchase #5	$6.97	13.227%	$7.8919	$7.89	$7.90	$7.90
Purchase #6	$85.30	8.272%	$92.356	$92.36	$92.35	$92.40
Purchase #7	$139.71	9.131%	$152.4669	$152.47	$152.45	$152.50
7 purchase totals =	$723.60		$794.7886	$794.79	$794.75	$794.90