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	$70.27	4.234%	$73.2452	$73.25	$73.25	$73.20
Purchase #2	$90.96	6.272%	$96.665	$96.67	$96.65	$96.70
Purchase #3	$104.33	13.693%	$118.6159	$118.62	$118.60	$118.60
Purchase #4	$239.60	13.283%	$271.4261	$271.43	$271.45	$271.40
Purchase #5	$35.32	7.288%	$37.8941	$37.89	$37.90	$37.90
Purchase #6	$213.87	12.465%	$240.5289	$240.53	$240.55	$240.50
Purchase #7	$16.95	12.818%	$19.1227	$19.12	$19.10	$19.10
7 purchase totals =	$771.30		$857.4979	$857.51	$857.50	$857.40