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	$29.75	5.562%	$31.4047	$31.40	$31.40	$31.40
Purchase #2	$152.82	5.861%	$161.7768	$161.78	$161.80	$161.80
Purchase #3	$59.46	13.802%	$67.6667	$67.67	$67.65	$67.70
Purchase #4	$78.74	9.511%	$86.229	$86.23	$86.25	$86.20
Purchase #5	$77.54	3.753%	$80.4501	$80.45	$80.45	$80.50
Purchase #6	$35.38	5.604%	$37.3627	$37.36	$37.35	$37.40
Purchase #7	$171.42	5.453%	$180.7675	$180.77	$180.75	$180.80
7 purchase totals =	$605.11		$645.6575	$645.66	$645.65	$645.80