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	$81.55	10.752%	$90.3183	$90.32	$90.30	$90.30
Purchase #2	$99.88	9.220%	$109.0889	$109.09	$109.10	$109.10
Purchase #3	$175.41	3.173%	$180.9758	$180.98	$181.00	$181.00
Purchase #4	$49.81	11.690%	$55.6328	$55.63	$55.65	$55.60
Purchase #5	$154.61	8.232%	$167.3375	$167.34	$167.35	$167.30
Purchase #6	$238.36	8.472%	$258.5539	$258.55	$258.55	$258.60
Purchase #7	$86.40	13.811%	$98.3327	$98.33	$98.35	$98.30
7 purchase totals =	$886.02		$960.2399	$960.24	$960.30	$960.20