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	$37.62	12.321%	$42.2552	$42.26	$42.25	$42.30
Purchase #2	$108.77	3.802%	$112.9054	$112.91	$112.90	$112.90
Purchase #3	$118.82	10.282%	$131.0371	$131.04	$131.05	$131.00
Purchase #4	$112.79	10.304%	$124.4119	$124.41	$124.40	$124.40
Purchase #5	$181.99	11.604%	$203.1081	$203.11	$203.10	$203.10
Purchase #6	$81.80	11.755%	$91.4156	$91.42	$91.40	$91.40
Purchase #7	$76.56	13.283%	$86.7295	$86.73	$86.75	$86.70
7 purchase totals =	$718.35		$791.8628	$791.88	$791.85	$791.80