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	$90.84	9.428%	$99.4044	$99.40	$99.40	$99.40
Purchase #2	$31.88	12.187%	$35.7652	$35.77	$35.75	$35.80
Purchase #3	$159.96	13.845%	$182.1065	$182.11	$182.10	$182.10
Purchase #4	$169.29	9.570%	$185.4911	$185.49	$185.50	$185.50
Purchase #5	$114.32	3.194%	$117.9714	$117.97	$117.95	$118.00
Purchase #6	$241.72	8.666%	$262.6675	$262.67	$262.65	$262.70
Purchase #7	$51.76	7.354%	$55.5664	$55.57	$55.55	$55.60
7 purchase totals =	$859.77		$938.9725	$938.98	$938.90	$939.10