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	$203.31	13.674%	$231.1106	$231.11	$231.10	$231.10
Purchase #2	$250.57	11.702%	$279.8917	$279.89	$279.90	$279.90
Purchase #3	$146.73	4.171%	$152.8501	$152.85	$152.85	$152.90
Purchase #4	$209.92	6.162%	$222.8553	$222.86	$222.85	$222.90
Purchase #5	$73.69	6.521%	$78.4953	$78.50	$78.50	$78.50
Purchase #6	$213.62	8.850%	$232.5254	$232.53	$232.55	$232.50
Purchase #7	$102.79	6.395%	$109.3634	$109.36	$109.35	$109.40
7 purchase totals =	$1,200.63		$1,307.0918	$1,307.10	$1,307.10	$1,307.20