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	$99.33	3.469%	$102.7758	$102.78	$102.80	$102.80
Purchase #2	$60.48	6.381%	$64.3392	$64.34	$64.35	$64.30
Purchase #3	$218.39	7.790%	$235.4026	$235.40	$235.40	$235.40
Purchase #4	$18.55	3.563%	$19.2109	$19.21	$19.20	$19.20
Purchase #5	$75.86	3.575%	$78.572	$78.57	$78.55	$78.60
Purchase #6	$189.82	11.102%	$210.8938	$210.89	$210.90	$210.90
Purchase #7	$37.80	11.370%	$42.0979	$42.10	$42.10	$42.10
7 purchase totals =	$700.23		$753.2922	$753.29	$753.30	$753.30