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	$7.48	8.652%	$8.1272	$8.13	$8.15	$8.10
Purchase #2	$250.32	9.624%	$274.4108	$274.41	$274.40	$274.40
Purchase #3	$164.47	12.769%	$185.4712	$185.47	$185.45	$185.50
Purchase #4	$56.51	5.229%	$59.4649	$59.46	$59.45	$59.50
Purchase #5	$31.29	13.561%	$35.5332	$35.53	$35.55	$35.50
Purchase #6	$141.28	9.114%	$154.1563	$154.16	$154.15	$154.20
Purchase #7	$182.54	9.666%	$200.1843	$200.18	$200.20	$200.20
7 purchase totals =	$833.89		$917.3479	$917.34	$917.35	$917.40