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	$115.30	4.600%	$120.6038	$120.60	$120.60	$120.60
Purchase #2	$239.79	12.760%	$270.3872	$270.39	$270.40	$270.40
Purchase #3	$47.96	13.443%	$54.4073	$54.41	$54.40	$54.40
Purchase #4	$167.90	6.466%	$178.7564	$178.76	$178.75	$178.80
Purchase #5	$198.32	6.828%	$211.8613	$211.86	$211.85	$211.90
Purchase #6	$71.82	9.415%	$78.5819	$78.58	$78.60	$78.60
Purchase #7	$86.74	8.285%	$93.9264	$93.93	$93.95	$93.90
7 purchase totals =	$927.83		$1,008.5243	$1,008.53	$1,008.55	$1,008.60