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	$234.46	12.753%	$264.3607	$264.36	$264.35	$264.40
Purchase #2	$49.81	8.869%	$54.2276	$54.23	$54.25	$54.20
Purchase #3	$94.55	6.434%	$100.6333	$100.63	$100.65	$100.60
Purchase #4	$56.79	4.606%	$59.4057	$59.41	$59.40	$59.40
Purchase #5	$234.37	12.765%	$264.2873	$264.29	$264.30	$264.30
Purchase #6	$154.29	9.245%	$168.5541	$168.55	$168.55	$168.60
Purchase #7	$120.70	6.762%	$128.8617	$128.86	$128.85	$128.90
7 purchase totals =	$944.97		$1,040.3304	$1,040.33	$1,040.35	$1,040.40