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	$167.76	12.861%	$189.3356	$189.34	$189.35	$189.30
Purchase #2	$142.80	3.442%	$147.7152	$147.72	$147.70	$147.70
Purchase #3	$110.77	9.125%	$120.8778	$120.88	$120.90	$120.90
Purchase #4	$165.36	4.628%	$173.0129	$173.01	$173.00	$173.00
Purchase #5	$94.71	9.105%	$103.3333	$103.33	$103.35	$103.30
Purchase #6	$89.96	7.219%	$96.4542	$96.45	$96.45	$96.50
Purchase #7	$216.97	8.687%	$235.8182	$235.82	$235.80	$235.80
7 purchase totals =	$988.33		$1,066.5472	$1,066.55	$1,066.55	$1,066.50