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	$138.40	9.341%	$151.3279	$151.33	$151.35	$151.30
Purchase #2	$213.88	6.808%	$228.441	$228.44	$228.45	$228.40
Purchase #3	$102.48	6.656%	$109.3011	$109.30	$109.30	$109.30
Purchase #4	$125.56	4.827%	$131.6208	$131.62	$131.60	$131.60
Purchase #5	$77.82	6.791%	$83.1048	$83.10	$83.10	$83.10
Purchase #6	$28.30	6.175%	$30.0475	$30.05	$30.05	$30.00
Purchase #7	$35.34	11.503%	$39.4052	$39.41	$39.40	$39.40
7 purchase totals =	$721.78		$773.2483	$773.25	$773.25	$773.10