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	$91.30	12.410%	$102.6303	$102.63	$102.65	$102.60
Purchase #2	$145.31	9.611%	$159.2757	$159.28	$159.30	$159.30
Purchase #3	$212.56	11.411%	$236.8152	$236.82	$236.80	$236.80
Purchase #4	$33.72	10.606%	$37.2963	$37.30	$37.30	$37.30
Purchase #5	$20.83	5.596%	$21.9956	$22.00	$22.00	$22.00
Purchase #6	$176.29	6.618%	$187.9569	$187.96	$187.95	$188.00
Purchase #7	$148.33	9.818%	$162.893	$162.89	$162.90	$162.90
7 purchase totals =	$828.34		$908.8630	$908.88	$908.90	$908.90